TL;DW is: he made these distasteful jokes in Twitch chat on one of the biggest tournament streams where he was a host:

The joke was kinda distasteful at first, but easy to shrug off IMO. But then he doubles down with a bunch more increasingly distasteful jokes that become harder to ignore.
He could so easily have apologised and I suspect everyone would have moved on. That would have been the end of it. But for some reason he has steadfastly refused to do so.
He initially received a 90 day suspension from Microsoft for this, later reduced down to 30 days. And he was removed from casting the Red Bull Wololo: Londinium tournament in April. In retaliation, he announced he's cancelling his weekly tournament and pulling out of aoe4 entirely.
IMO, it says a lot about the guy's character that he refuses to make a simple apology here. There's just no reason not to.