There is a lot of politics behind who gets on the main card, that usually has to do with MMA teams and the trainers pushing for one of their guys for a main card slot. So if some one gets bumped from a main card Joe Silva will call up a manager of a team and promise the next card will feature of the team fighters on the main card. Really has little to due with ratings a lot of the time.
The joke is not always the show, but Zuffa and what they have done to this sport, while people credit them for making the sport big and popular they have as well really put the fighters in a bad spot with the way they manage the fighters and their lack of respectable treatment of them. It's just flat out exploitation. Zuffa controls who sponsors you, if they don't like a sponsor you have they will tell you to drop them or cover the sponsor on your shorts or just cut you. It's really fucked and I was at the fighters summit a few years ago and it's just total shit. They make you manage all your social media and play their game exactly like they want you to or they cut you. It's really a bunch of shit these days.