Is it because most teams from low majors pretty much lose every non conference game? So when it comes to conference time, they can only play teams who have lost all non conference games? Where as a bad team from a power 5 losses most conference games, but at least they lose to teams who won most non conference games?
So a 300 team becomes a 300 team by playing in a conference who losses all of their non conference games then losses all the in conference games to the teams who lost all their non conference games. Where as a 200 rpi team comes from a conference who wins more non conference games (against terrible teams more than likely), then finishes somewhere in the middle of their weak but not terrible conference.