This goes hand-in-hand with M-1's apparently poor management. Why didn't Fedor join the UFC? M-1 said the contract wasn't good enough, but all Fedor had to do was step up to the plate.
Fedor is a modest guy, but aside from his excellent strikes and his ability to reverse impossible positions, he's pretty boring. Not saying he should be a hype train and become another Andy Silva (e.g., Silva vs. Maia), but a little excitement would be good for his fans.
The thing is, Fedor knows he doesn't need any extra marketability. A lot of fans have deified him so much that they probably bow to a statue of him before each practice.
Fedor is the least interested in hyping things, and being that he's off and on with considering retirement, it's likely that fans will go on wondering if "The Last Emperor" had it in him to beat the best in the UFC, for instance. Perhaps Fabricio Werdum beating his brother will show a different side to Fedor that we haven't seen before.
One way or the other, if he doesn't go into the UFC, we should at least see him commit to Strikeforce and face the best it has to offer, which includes Overeem.