By why are they willing to pursue it? Part of it is a misguided love of science above everything else, perhaps, but part of a person's ability to rationalize doing multiple postdocs upon postdocs at all is that they can potentially ultimately obtain a permanent position. If you were to take away the permanence of that position, then it becomes harder to rationalize spending so much of your life to go after it. If professors then start getting fired because they no longer have that job security, then it becomes much
harder to rationalize to yourself that you should spend all of your youth going after this job. Sure, some people will still do it, but I think most people would opt at that point to look at more lucrative options, since you'd have just as much job security in industry but a much higher salary. A love of science can only carry you so far. I think that the number of quality candidates going after faculty positions would drop in this case. As a result, to really remain competitive with industry, the salaries of non-permanent faculty jobs would have to go up - or hiring from other countries will increase. If university administrations could get away with eliminating tenure without increasing salaries or foreign hirings and still have quality candidates, why haven't they tried?
To a certain point I'm sure you can decrease a tenured prof's salary and people will still chase the positions, but there is a limit to how much you can decrease it - and that's if the position is permanent. If the position is not permanent I suspect that eventually the salary will have to increase to remain competitive with other options, all other things being kept the same.
Under the current system you can exploit some people all of the time, but if you change the system by removing one of the best 'rewards' of the long and arduous process of getting a faculty position, I think most people won't be as willing to be exploited anymore.