Some... perhaps most... players jump into the portal, but some are pushed.
Coaches and programs used to have so much more unbalanced leverage because of the sit-a-year rule, intra- conference prohibitions, etc., while they themselves had only whatever mobility restrictions they had contractually agreed to (and even then, those could be renegotiated without ncaa interference), whereas the players had the coaches playing good cop and the ncaa playing bad cop.
That imbalance caused the collapse of the power of the bad cop part of the equation, but the 'good' cop side is still working through the transition, with some quicker to take adaptive advantage than others, but still with the underlying sports culture advantage of being seen as the good cops.
While coaches stand on the shoulders of the program employing them, it's primarily the coaches who establish the relationships with players that can be leveraged through loyalty... usually far more to the coaches than to the program or school at large... so coaches can still leverage loyalty to themselves, while swapping their financiers. Multi-year contracts between players and programs would help level some of that, making it more costly and complicated for coaches to use player poaching to increase their own mobility value, and it would simultaneously protect players from being used quite so temporarily (less pushing out players, more incentive to develop who you have), and also instill more responsibility to the players to live up to their promises.
Of course without a legislative framework, there wouldn't be a way to keep some from gaming it and undercutting what would be best for the whole game.
