It's not the decision I would have made if I were Eric because I love BYU and would have jumped at the chance to be a legendary sports icon (unfortunately I'm a slow-twitch 5'11" dude with 24" hops, so....engineering is all I got). But I don't see why it's so hard to understand why a guy like Eric would make the other choice. That's a pretty good life.
All of the reasons you state for why he should have stayed are great for you making your own life choices. That's how I would have thought about things too if it were me. But they are obviously not compelling reasons for Eric or he would be coming back for his JR season.