It wasn't that this player was disrespectful/racist/etc., it's that they were so much better that playing against this player was almost a guaranteed loss.
this player was at the top of the matchmaking ladder
that (very small) population had a lot of people who wanted to avoid him
he couldn’t get games at his current level, and he couldn’t rise above that level, because there was nothing above that level
Which is a normal part of a competitive multiplayer game, except that people got the option to avoid him (rather than learn to beat him), so many took it!