Your assumption that good players would want more

eligibility might not be right. Any good player that wants to play in the NFL leaves after 3 years, redshirt or not. Many top players would go pro after their freshman or soph seasons if it were allowed.

In addition, at most schools, players buried in the depth chart end up transferring. Why would they want to be further buried by another level with 100 players on a team?

ND is a bit of an aberration in the P5 in that most of our guys are 4+ year players, even if they have NFL aspirations. But that's not necessarily the case elsewhere.