The thing that I don't buy with this Brock Lesnar conspiracy theory is that Brock is a prideful person, he likes to be the best at what he does, otherwise he would probably still be in the WWE if he wanted easy money.
Brock's bank account must be stacked also, he probably doesn't need one last final payday from the UFC. He and his Wife both worked for the WWE, both made millions of dollars. They live a laid back lifestyle in the country, so they probably don't have too many huge bills to pay like other athletes/millionaires.
Brock Lesnar also started working out for this fight, he visited Randy Couture and trained with him for a while. That would be going to a lot of trouble and unnecessary workouts to make this plan. He wouldn't need to be training at all if this was really how it all worked out.
Maybe he did it as a good gesture to Dana and the Fertita's for helping him be on top of the MMA world in record time, giving him a shit load of money and helping when he was on the verge of death.
I can buy this story, it did seem like after the cain fight he wanted no more of it and then out the blue he was in a no1 contender fight with JDS and a coach on TUF 13. I dont know if its true or not, but certainly is a little suspicious. But on the other hand i dont really care, we get to see a better fight and Brock was probably a better personailty to have than Carwin on TUF 13, although i would of prefered it if Mir was the other coach.