Miramonti
Lifer
He is fighting in Strikeforce because he had a contract with them. And when it was time to switch over, he still had contractual obligations with m-1 as his promoter which wont let him fight in UFC.
The whole thing is kinda silly, but everyone wants their piece of the pie.
Fedor had never fought in the UFC before because Dana was unwilling to make many concessions to the contract (until recently, although too late). He likes to keep a tight reign over his fighters.
It goes beyond reigning over his fighters. He'd only have Fedor for a few fights, but its his 'vision' for what he wants UFC to be that killed it imo. Co-promoting gives publicity to other mma entities than the UFC, and that's the last thing he wants to open the door to.
Iirc, he owns 10% of it, and he wants to build the UFC as high as it can go. Fwiw, he's done a helluva job so far. Hypothetically, if a Lesnar/Fedor fight goes down thru a co-promotion, and Fedor wins, UFC image also takes a hit when they undeniably won't have the title holder and best HW in the world, and I think he wants to avoid that possibility, and/or capitalize it if Fedor fights for UFC.