When you have 4-5 stars arriving each year, and 4-5 more nearly that, they expect to play, early and often. Attitude then becomes a key along with ability to learn and pick up the playbook.
Then you likely have at a place like Bama 8-10 3 stars, many of whom would start by their 3rd year or so at UK, but play STs some and sit and get pounded with the twos at practice. I doubt a coach has to tell them, they can see they won't play as a 4th year, much if any.
Obviously, at "UK", they get 3-5 4 stars and no fives. So, a 3 who works pretty hard has an excellent change of starting in his final year, we all know this. Ohio State should have almost the same issue (as Bama).