Thank you everyone for your very good responses.

And I quite agree that this is a real challenge. Especially since what I have in mind is that direct health concern is a major contributing factor, say at least 40%. Alright, some ideas I have:
1) maybe the phase out starts at the high school level with cost being a big factor, and with some doctors saying, Given these new studies I can no longer sign off on football and give it a clean bill of health,
2) and maybe that's the way it plays out in the face of uncertainly. Instead of banning football seeming like the active step, maybe signing off on football becomes seen as the active step for which we don't have enough information,
3) families are in general considerably more pro-education. The GI Bill is the major contributing factor for this angle, with other interesting minor contributing factors, (*even though repeated head trauma often causes such things as impulsiveness, poorer emotional skills, poorer executive functioning skills, etc. Let's say this part is at first not well understood),
4) per jahenders above, the idea that football profits should be plowed back into the university might slow down the growth of the major powerhouse programs, and
5) there is an interesting sidenote I read that in around 1960(?), at one of the major schools, maybe Notre Dame(?), or maybe Ohio State(?), or one of the other major programs, the president of the university cancelled the team's participation in a bowl game for which they had earned a spot, citing as his reason that students were over-emphasizing football ? ? ? I mean, it's absolutely incredible. It's something that's almost unimaginable today. Perhaps he just didn't lift his university's rule against bowl participation like he was expected to lift? But no, I think he actually cancelled. Will try and look this up.
*I might be thinking of Notre Dame's resurgent 1964 season, the first with Ara Parseghian as head coach.