The simplest and most direct answer is that most people have not heard of that paper. But I would like to dive into a slightly deeper analysis and say that the paper itself has a wrong result. Without even reading the contents, I can already debunk the abstract. It claims that re-working the equation can yield a very substantial chance of there being not one single interplanetary civilization in our galaxy, and without even invoking a "yet".
Now as this paper, the Fermi Paradox, the Drake Equation, and many other sources have correctly surmised, calculating the probabilities are fraught with too many unknowns to yield a reasonable result. But what they all seem to miss is that the probabilities we can best rule out are the most extreme ones. We can narrow down the possible ranges to fields many orders of magnitudes across, yet still far narrower than a complete guess. Doing so can actually rule out some guesses entirely.
As one example, we don't know if life can exist in very many circumstances outside our own, but there is a range of circumstances in which we know that life can exist, stable enough to last for billions of years yet unstable enough to provoke gradual evolution. Furthermore, we can speculate significantly on the availability of such environments within our galaxy. We know that the primary factors leading to our home and its stability are:
1.) third-generation star with high metallicity (with accretion disk containing substantial iron fraction) of spectral class K, G, or F
2.) circular orbit within "Goldilocks" zone, with large moon at small distance
3.) local galactic habitability (not being in a sterilization zone such as with strong gamma radiation present)
possibly 4.) shepherd planet like Jupiter orbiting outside the "Goldilocks" zone
All other major factors are known to have a high likelihood or near-certainty of happening, such as stable planetary magnetic field (assuming it's an iron-core planet), presence of surface water and wide variety of lighter elements, abiogenesis within bio-stability timeframe, evolution due to natural selection, planet failing to be sterilized in major extinction events due to large variety of life across different types of habitats.
We know that a prospective star ~5 billion years ago (or ~10 billion years after the Big Bang) within the Milky Way galaxy has a pretty high likelihood of being the right spectral class and with high enough metallicity. While the vast majority of stars in the size range have low metallicity at this age of the universe, there are nonetheless at minimum millions of stars within this range just in our own galaxy, forming ~10 BYA after the Big Bang or earlier. Planetary systems around stars of high metallicity should have an extremely high likelihood of containing large amounts of iron, due to iron's position at the fusion peak--thus formation of planetary elements within a supernova will always produce substantial amounts of iron. We know many examples already of planets within the right mass range and within the "Goldilocks" zone--this is a highly likely occurrence. Estimates for galactic habitability are generally high as well; given how many times our own planet had to orbit our galaxy, it is extremely unlikely that greater than half of the galaxy lies within uninhabitable regions. So the only remaining factor is chance to obtain a moon like Earth's. This last item could be very rare, but planetary models eliminate it being more than a few orders of magnitude down. So you still have at absolute minimum hundreds of planets within our galaxy forming long-term life 5 BYA or earlier, and having pressured that life into evolving up until today (or occasionally, until its host star grew too bright and sanitized the planet).
While we have little to explain the true likelihood of life achieving the ability to exit its home planet (within its stability timeframe and prior to the current day) under these conditions, we can point to perhaps 1-2 dozen major evolutionary breakthroughs in our own evolution which led us down this path. Examining every single one, we consistently find that life took a path of fairly low resistance--while it may have taken trillions of chances to get the mutation that started the next wing of development, it always bridged the mutation gaps in bridges the size of one single mutation. What can appear to us at a glance to require three or more simultaneous and cohabiting mutations will, virtually unfailingly, happen anyway one mutation at a time. Maybe it's just the universe we live in, or maybe the apparent extreme unlikeliness hides a plethora of other extremely unlikely options of which anyone could have pushed us forward. But one way or another, no matter how many branches reach an evolutionary dead-end, there are always those that don't, and they always dominate the next niche. Our evolution toward stepping into the stars may have been nearly guaranteed, and at minimum we can cast some VERY strong doubt on its likelihood being extremely low.
So given a lower bound of perhaps hundreds of worlds like ours beginning greater than 5 MYA (more reasonably thousands to tens of thousands), and given an ever-increasing rate of these worlds forming as the universe and the galaxy age, and given the relative ease with which a planet like ours can produce people like us within the available time frame, we can cast strong doubt on the lower bound estimate of ~50% chance we're alone in the galaxy, and virtually eliminate any figures pushing higher than 90%, regardless of their methodology. They can't be right. Here I have demonstrated that Enrico Fermi was right in proposing that our galaxy contains many spacefaring civilizations; we can be relatively certain that it indeed does. But perhaps more importantly, we can dispel the Fermi Paradox easily by looking forward rather than backward: there are two assumptions which it relies upon, both of which are extremely unreasonable to the point of invalidating the proposition outright and suggesting that in fact, regardless of how many interstellar civilizations there are in our galaxy (even millions!) and how old they are (billions of years!), we should actually fully expect to NOT see any of them at our current tech level.
The first assumption is that we will expand into our galaxy on a timescale too short to be significant relative to the age of the universe. But as faster than light travel has been absolutely thoroughly debunked and as we gain a greater understanding of the needs of habitation in space, we see more and more that it doesn't matter whether we use robots, engineered life, or any other advanced technology, there simply isn't a way to maintain the expansionist mentality itself during space expansion. Ecology trumps expansion to such an enormous degree that no civilization can thrive in space (due to physics, regardless of genetics) without fully embracing an ecologist mentality. Each new position we occupy must focus predominantly on its own maintenance, and will only support a robust spaceship industry after it has been developing for a very long time. Spaceships will sluggishly drift through the stars on not-so-insignificant timescales. And we will be forced to come to terms with these limitations in order to thrive out there. Will we expand on timescales in the thousands of years? No. It's not physically possible. Will we expand on timescales in the millions of years? Again, no. This time it would be physically possible, but it would require devoting all resources toward expansion while simultaneously fully understanding and embracing the futility of that mindset. No race of people intelligent enough to expand into space won't abandon expansionism when in space. So we will expand across our host galaxy on timescales of billions of years--and given how long it took for people like us to step into the stars in the first place (~10+ billion years), it's entirely expected that our galaxy is less colonized than not.
The second assumption is that we could see them if they weren't very far away (~1-1000 light years) yet the brightness of a beacon capable of signalling us at those distances is so enormous as to be completely absurd to expect anyone to build such a thing. What would it be for? To signal to young civilizations that they aren't alone? If they're dying to know, they'll figure that out probably within a few thousand years when they start making solar-system sized collector arrays (already within our tech level), and can detect signals SEVERAL orders of magnitude fainter than what SETI can detect today with a planet-sized collector array. Since these civilizations take billions of years to crawl across the galaxy, they have no reason to make enormously bright beacons just to say hi to us when we can't even respond. No, they will communicate with lasers, direct to target. If they wanted to say hi to us, they would do it with a laser, and they would leave it running for bursts of decades or centuries at a time. SETI already failed to find such a communication within its first major sweep, so there's little reason to continue looking at this point, to be honest. I say that not with high likelihood, not with extremely high likelihood, but definitively. It can't not be true. Extreme projects of extreme stupidity in design don't happen at all, anywhere, because of the way intelligence works. We can be as certain of this as we can be of the Boltzmann Brain hypothesis being wrong.
