BicycleTree said:
1.) who could drive to a bus stop, if such a stop were feasible for the bus company to create given that people who could use it were willing, in their town or in another town closer in that the bus stops at, and who both go to work and return from work during rush hours (more people than this could do it "without much trouble" but let's cut things clean)
2.) let's say 10 people as a lower bound
Well, with the long series of conditions required for (1), I'd say slim to none.
As for 2, do you mean 10 people per bus, or 10 people in a town, total? If it's 10 people in a town, it's not even worth running a bus. If it's 10 people per bus going from the same origin to the same destination, maybe 100 people total to make it worth running 10 or 12 buses a day, assuming they can be concentrated during the rush hour travel time and all 100 people fit the criteria in (1), then that might be worth running a bus route for.
Though, if there's just one bus worth of people, then it's probably not worthwhile. The reason is that there's no flexibility at all. If you miss your bus, you're stuck. Not a huge problem if you miss it in the morning and can go back home and drive to work (except that by then you're probably already late and the extra time to and from the bus stop would make you even later), but a really big problem if you miss the bus home and don't have any other way to get back home.
Setting up a busing system and routes, even just adding one route, is a lot more complicated than you seem to think it is.
On a smaller scale, if you really mean just 10 people, then solutions other than buses work better. Some towns have smaller carpool lots near interstate or highway on-ramps. So, if I can locate a group of people who have compatible schedules with mine and are going to a close location to where I am headed, instead of driving all over town picking up people for a carpool, you can meet near the freeway entrance and everyone else can park their cars and the driver for the day drives everyone in. This gives more flexibility at the end of the day. If one person is running a bit late, you do get stuck waiting for them, but at least it's not like running for a bus that won't wait. In addition, if you miss your carpool in the morning (if people need to be at work at a certain time, they can't stand around waiting for the one habitually late person), then you already are in your car and on the way to the freeway anyway, so you're not stuck anywhere without a ride or being made any later like if you miss your bus in the morning.
In some places, there are efforts to help people find carpoolers.
But, this still doesn't solve the problem of increasing numbers of people who are combining their trip home with half a dozen errands, and all the other assorted reasons that prevent someone from traveling a fixed daily route on a fixed schedule.