You team's enthusiasm has a lot to do with it. If you compare your team's first game from last season to your team's first game this season, your ratings are significantly better. Plus your tactics have a big impact on the team ratings. If you play a motion offense, your outside scoring rating will be better and your inside scoring will be weaker.
The ratings are also heavily weighted to the positions they are typically associated with. If you play guys out of position to take advantage of matchups, you might have slightly lower ratings, but outperform those ratings.