Doesn't he work for them?
The entire notion of the American sports commissioner started when Kennesaw Mountain Landis was appointed following the Black Sox scandal. A commissioner is (or at least was) supposed to be the guy above the fray, a theoretically independent guy with the best interest of the sport at heart. This may sound crazy if you're under 30, but believe it or not, there used to be a time when all the various commissioners would sometimes take action that ran against what the owners wanted. The owners employed the commissioners, of course, but they weren't always just a rubber stamp for what the owners wanted.
Eventually this mostly died, of course, with the most egregious milestone being when the baseball owners fired their commissioner and just appointed one of themselves to the job. Baseball effectively hasn't had a commissioner for 30 years. The other sports at least have the pretense of having a semi-autonomous robot in place.
Bettman is the worst (or, arguably, the best) modern commissioner [1] because he has literally no independent presence at all. He is not there. He is a focus of hate for the fans, and that is all. The owners screw the fans and the fans boo Gary Bettman at the All-Star Game and nothing ever changes.
[1] Other than Selig, of course, who does not count.