Many non-athletes take more than 4 years to get a college undergrad degree. Some can do it in 3 years.
If you had a rule that students were eligible as long as they were students, they could play for years.
As long as the only reward for playing college sports was a scholarship for education, it could make sense for it to be for 4 years.
Now with NIL collectives, which are paying athletes salaries, the athletes can make the case that if you limit them to X years, you are depriving them of potential income. If they are employees, why cut them off?
That's the argument being made in some of the lawsuits currently.
College leaders will have to decide whether they want to operate professional sports leagues, or be places of education where some students can play sports.
In the sports which have actual professional leagues, the incentive would presumably be to leave college and go pro, as it is today. But for the ones who don't get drafted, staying "in school" and getting NIL money makes sense.
Personally, I think it's all disgusting. The only thing going for it, I guess, is that the athletes would still have to stay academically eligible. But that's not hard to do; schools with grad players have very minimal academic programs for those students to remain eligible.