Just because he does it all the time and is guilty as sin doesn't make it easy. This isn't hockey, goons like him aren't easy to find because it's been long since legislated out of the game. Someone like Grant goes and just hammers someone, odds are he's gonna get a massive suspension, and won't even do it right. Anyone that does it wrong risks losing millions of dollars in current and future earnings, it's not easy to find someone like that.
The guy to do it would have been someone like Haslem, or maybe Giannis' brother. You need someone who really doesn't give a shit, doesn't have much of a future, and is big enough and coordinated enough to make it count (part of what makes Draymond so good at violence is that he's both very fast and very strong). It's harder than we think to find that guy (and it's definitely not Tillman, or anyone on the Celtics roster currently).