Otherwise, why waste a scholarship on someone who is never expected to see the field. Sometimes the player doesn't develop as well as expected. Sometimes better players are recruited behind him, keeping him out of the starting lineup. Sometimes a player gets in legal trouble, and can't make it back onto the field. Sometimes a player doesn't want to do the work to be a successful Div-1A athlete, much less a P5 player. There are a lot of reasons players just don't live up to expectations when they first signed.

The majority of players hitting the portal are guys who want more playing time. You rarely see a starter, or a projected starter hit the portal.