I wonder if it just comes down to the old rule of comedy, offensive jokes are only offensive if they're not funny. It's always been a bit unfair. If you make a good faith effort to do "edgy" comedy with borderline offensive material, but the humor just doesn't work, you get all the heat for using rough language, bringing up insensitive topics, etc. But if you just happen to be talented enough to make the same material funny and make people laugh, people don't hold any of that against you. So, QT can get away with these things if his movie works as entertainment. But, yeah, I imagine from a production standpoint, if someone without that track record of making "insensitive" movies without inspiring a backlash tries to make a movie with risky content, the studio is going to reject it. Being a successful director always gives you more power to do things that the studios would block from an average director.