A couple of things might explain this:
1. We lost a ton of players, so our rankings for those years are very inflated if you count people who stayed.
2. Star ranking doesn't take into consideration how well a player will fit the needs of a team, just how good the player is. Switching offensives and defense every other year makes the players recruited less helpful relative to established schools like Iowa and Wisconsin who use their players exactly as anticipated.
3. And I hate this one. There might be a tendency of players with higher star rankings who pick lesser schools because they don't want to work as hard to get playing time. So the 5* who chooses not to go to bama and instead goes to crappy other school might be because he doesn't take football as seriously, but still wants a basically guaranteed starting position. How hard they try/ how seriously they take the game obviously can't be accounted for in the star rankings.
Just some thoughts