Some sports have age minimums and/or time requirements for years out of high school. Football and basketball do, swimming and soccer and golf do not. No one seemed to have a big problem when Tiger left Stanford after his sophomore year to go pro. No one accused him of taking another student’s spot.
Many of the great players stay through all 4-5 years of eligibility and others don’t, even at Stanford and Harvard and Duke.
At least in the Pac 12 (not sure if it is all Power 5 schools), any scholarship athlete who plays at least 2 years has the right to finish his/her degree. I think some who go pro will do that if only because they have promised their moms. Larry Fitzgerald finished at U of Phoenix. I think Christian McCaffrey will finish his Stanford degree, mostly because he comes from a family of athletes who all have college degrees, most from Stanford or Duke.