I have a theory on one reason why Michael Oliver and others might be giving Arsenal so many red cards.
I think the referees are told to not give in to fan pressure or questioning of referees. So Oliver doesn't want to show any favour toward Arsenal, as in their mind this would be conceding to pressure. He wants to show junior referees and the world how to be resilient and strong.
So, subconsciously, he looks to punish Arsenal. The first chance he gets to showcase resilience, he goes for it. This would also explain the speed with which he gave Skelly the red card, and why VAR didn't overturn it.
TLDR: PGMOL want to show that they are the boss. That they won't be influenced by people questioning the referees. In trying to show this, they are subconsciously biased the other way.