Well, if he feels he needs to train specifically for Dos Santos, he's probably not going to feel confident going in to the fight on short notice.
But when he was due to fight Velasquez for the belt - that got scrapped - and Miocic was the replacement, he cited a long standing injury as his reason for pulling out, which seemed a bit strange.
I wonder if Werdum feels because of their first fight, he has Velasquez's number. I'd see it being completely different than the first fight - especially on the feet.