You can't have an agent in the NCAA. If you could, then your argument is valid. I'm going to assume you are fearful that would happen. It might could, but you'd still have other rules in place to debate that are stupid, too...like having to sit out a year or so per eligibility and such. It all rolls together into a bigger ball of a problem that is this...
Only the athletes at colleges, never any other kid on scholarship going to whatever college that has to deal with these issues. Why? The easy answer is because said colleges want them on their team (which is why they recruited them to annoying degrees in the first place, obviously) so that their team wins and their team makes more money. Money, money, money. They go after these kids as early as 12 years old these days (even younger per AAU basketball, now) for the express purpose of dollar signs. Why should you ever expect a kid or their parents to not want some of the mass profits, too? It's insane to expect otherwise.
Oh, and certain colleges have unfair advantages already, anyway. Minnesota doesn't have the prestige of Alabama, for example. Bring money into the equation based on prestige percentages, and Alabama wins easily again. BUT...think of this...what if it becomes an NFLPA/CBA type of pooled/equal percentages system? Then, suddenly, every team can only offer the same pay only. That levels the playing field like it has never been before. Then...Minnesota can pay a kid the same thing Alabama would...and that kid may well stay at Minnesota making them far more relevant.