A ref can justify a flag on every play. There's contact and holding by DB's on nearly every pass play. So, like in basketball, it has become subjective.

Of course, the players know this and learn to test the gray areas constantly. This makes the referee's job nearly impossible.

Finally, the players also know that the refs (in all sports) tend to swallow their whistles at the end of close games, especially championships. So they play more aggressively.

I don't think any of the inconsistencies are conspiracies, just human nature. Refs at Cameron get caught up in the excitement. And look at how exaggerated basketball refs now make the offensive charge call (a call that I think they often get wrong).