After losing badly to Stipe Miocic at UFC 161, Roy Nelson was believed to be on his way out of the UFC. It was the last fight of his contract, and while fans may love his portly shape and powerful right hand, there was obvious friction between Nelson and UFC president Dana White. Nelson received a new contract, a co-main event fight against Daniel Cormier at UFC 166, but still continues to talk about how poorly the promotion has treated him. Via MMA Junkie:

"Roy has this belief that we won't give him a title shot," White said. "We just won't do it."
Dana argued that the reason that the UFC hasn't given Nelson a title shot is his inability to win a fight that merits a title shot:

You've got to beat the guys to get a title (shot)," White said. "He's never beat the guys to get himself in line for a title shot."
I think Dana is 100% correct. Nelson has been given multiple fights against proven contenders and has lost all of them. He was destroyed by Junior dos Santos, ragdolled by Frank Mir, and comprehensively beaten by Fabricio Werdum. Stipe Miocic is not considered a title contender and Nelson was dominated by him, too. And at age 37 with 27 pro fights and nine years of pro MMA under his belt, the odds of him -- yes, even in a division as thin as heavyweight -- reaching top contender status are just about slim and none.