Ok, well from 1992 until probably 2010? We were pretty shit more often than not and United were the dominant force in football.
If we played a team significantly worse than us 50 times, how many times will they get in our box and we make an error/foul that leads to a penalty? It'll hardly happen,
On the other hand, if we're vastly better than them, we're gonna be in their box (ooh err) for most of ever match and they're going to mess up.
This is as much to do with the skewed penalty stats as anything. Better teams get more than bad teams because they get in positions to win them more often.
THAT said, in addition to that, you had a squad of players clearly drilled in the art of applying pressure to the referee, a coach who questioned the ref before the game even started and 75k baying fans.
What this goes back to again though is that refs are the problem, not the league, They don't tell a ref before a game to make these absurd decisions. If they did, they wouldn't have allowed VAR to show them all up even more.