Much of Cross' schtick is to be a jerk. Although it's true that he has animosity to the CHIPMUNKS, at the same time his attempt at being humorous is showing through.
Also, he signed up for three movies. But seriously, did ANYONE expect the first one to make such a shitload of money? With that said, I think he was as surprised as the rest of us that there even IS a third movie.
It's a paycheck - and he should be grateful he's making money in film/television - but I also think he's poking fun at himself for cashing in.