Brock was a huge PPV selling machine for sure, but you're also leaving out UFC 158 (St. Pierre vs Diaz) that did 1.1 million and UFC 66 (Ortiz vs Liddell 2) that did over a million.

Big names sell big PPVs for each sport. It's the same with boxing. Check out boxing's PPV numbers.

Pay-per-view - Wikipedia, the free encyclopedia

To find a PPV that cracked 500k buys that didn't feature the name De La Hoya (retired), Mayweather (nearing retirement) or Pacquiao (nearing retirement), you have to go back to 2003 when Roy Jones fought John Ruiz.

The problem with boxing is that it has all it's eggs in one basket. It has a few big names that draw a lot, but those are near retirement and there aren't any real stars set to take their place. Take those guys out of the picture, and PPV revenue is few and far between.

The UFC puts off a show nearly every week (not PPV), I reckon on average about 2 PPV's a month, and they CONSISTENTLY gather several hundred thousand buys. Like I mentioned earlier, UFC 170 did about 400k buys and it was one of the worst cards in recent memory. It was plagued by injuries and fighters dropping out of big fights, and it was headlined by two women fighters. And it STILL outdrew Canelo.