The amount of money they made saved their 2017 year. Plus, Conor wasn't going to defend against Ferguson, then Khabib back -to-back. He is not built for that type of action.
Conor is a matchup type of fighter. You match him up with 3-and-something and short notice opponents, and let him do his thing. Everybody wins. His fans buy the PPVs and fill the arena. He puts on an entertaining performance, and everybody wins.
That is how you use a piece like Conor. You don't put him up against 10 fight winning streak fighters, and then 9 fight winning streak fighters. Tony Ferguson fought 5 hard rounds at high altitude. Khabib can wrestle hard for at least 3 rounds. Conor ain't built for those types of problems.
The UFC will learn this, and start to take better care of their cash cows. Some fighters are good for the mainstream e.g. Conor, and some fighters are good for the underground e.g. Khabib and Tony.
It is like music. Conor is like a Jonas brother, maybe he can play his little guitar and get the mainstream excited, but he doesn't play anywhere close to Yngwie Malmsteen, who is more technical but less popular in the mainstream.
That's how life is. Some talent is for the mainstream and some talent is for the underground. It is rare to find a talent that bridges the mainstream and underground.