It's the drip drip drip of routine decisions that is more significant than the big decisions for me.
Every 50 50 in the central part of the field invariably goes to the 'big 6/7/8' team, the bar for what is a foul is different depending on what team you play for. And it's easy for refs to get away with as no pundit calls out a soft decision for their darling teams but jumps on any against them.
This in built advantage keeps the pressure up all game, and often leads to yellow cards that reduce a players effectiveness.
It's all these little things that lead to the unfavoured teams having limited ability to either hold the ball or win it back (not Everton, we just can't do those things).