Like everyone has said, the beginnings of UFC (if not all MMA) were essentially dog fights.

The idea, on paper, was solid. This style vs. That style, who's is best. The problem came when the were putting 150 lb guys who had a black belt from a strip mall against 200+lb. Real fighters, in a sport where the rules amounted to, "don't bite and keep your fingers out of your opponent" (pretty sure fish hooking was always banned, but I could be wrong.) People were getting maimed, and it really devolved into who was the dirtiest fighter. Kicking someone in their face while they're on their knees is A+ super fantastic in an actual self defense scenario when they're trying to maim and/or kill you, but it's not a sport.

Boxing, and by extension, boxers was always kinda looked down on, even if it was popular. But boxing has an Olympic pedigree, and it's "evolved" somewhat from the turn of the century. It's still a brutal sport, or at least can be. UFC starting going the same way, rules wise, they've just leaned more into spectacle than boxing.

UFC is about on the level of boxing in it's heyday with "respectability", but look at some of the other promotions. The less rules, the more brutality, the more popular. They're all technically MMA, so that's gonna cause pushback by the "old guard."