For one, it's not just established players that seek out long term deals. Ronald Acuna is one example. For many players this is life changing money, and they'll happily take the guarantee.This makes it sound as though proven, established players who want security are the same as developing players about to enroll in college. I think it's just as likely that a college player over-performs as underperforms. If they develop, they're the ones who will look at their long term deal and want out.
I personally don't see multi-year deals working in college sports, or if they do, as an exception. I don't see either side being happy enough with multi-year commitments. And an unhappy player isn't worth nearly as much as when they're fully bought in (pun intended?)
The real question is, do you think the status quo serves players better?
Look at the cases of Matthew Sluka at UNLV or Jayden Rashada's lawsuit against Billy Napier, and tell me that a written contract wouldn't have benefitted the players. Right now everyone is operating on nothing but promises.