Ehhh, I just think some of the refs in MLS have some ego issues and sometimes allow themselves to get caught up in the emotions of a game and allow that to effect how they call it (Chapman).
I think there are also many MLS refs that are too stubborn that once they make a decision, they will not budge from it, no matter what (see Chicago-Columbus match last night) and this is one of the biggest reasons why VAR is still so frustrating here (used so damn inconsistently).