Why should he care to be in the UFC or to fight Brock? To him Brock is just another body, in case people haven't gotten it by now I don't think Fedor cares who you put him against...
With that being said the only other thing he has to look at is the payday. He made as much fighting Brett Rogers as Brock did fighting Mir so to him I'm sure it doesn't matter where he fights and is probably less inclined to fight for the UFC because they aren't going to fork out a $400k payday for someone on their first fight. I don't blame him for staying where he's at.