The biggest problem is that they started advertising the sport not by accentuating the skills of the fighters but by the amount of childish insults per minute they can deliver. The pre-fight antics became more important than any possible outcome in the octagon.
If you look back, Chuck Liddell couldn't string two sentences together but you knew when he got into the cage, violence would happen. We weren't salivating about Chuck vs Wanderlei for years due to their thrash talk.
For an example of how far the sport has fallen, take UFC 92:
Frank Mir vs Big Nog, a long time Pride Vs UFC dream grappling match-up
Rampage vs Wanderlei, the third fight in one of the most violent trilogies ever
Rashad vs Forrest, two Ultimate Fighter winners
That event sold 1 million PPV buys.
There's not one big star on the card but there were three highly anticipated fights. We have come to a point where it's completely irrelevant how skilled the fighters are, if they're not controversial, they're not becoming stars.
To make matters worse, the company has completely lost the ability and integrity to set-up proper championship fights. Being a champion has become a marketing tool not a symbol of being the best. The fact that Conor-Ferguson is not a certain thing underlines this.
Ferguson has TEN wins in a row and he still doesn't have a proper title shot. You know who was the only other fighter that also had 10 wins in a row without a title shot? Max Holloway. Why?
Because the UFC let Conor to do whatever the hell he wants, which in his case is, paralyzing a division and never defending a belt.