Joss Whedon recently spoke to IGN about Avengers: Age of Ultron and several other topics. He talked about why a standalone Hulk film featuring Mark Ruffalo hasn’t happened yet and attributed it to rights issues between Marvel and Universal.
On Why There Hasn’t Been A Hulk Solo Movie In Several Years:
“Honestly I think it’s a legal thing. I think it’s because there’s other studio rights and this and that. It’s difficult. Hulk movies are very difficult because it isn’t a classic superhero story. It is more of a werewolf story, and finding a way to thread both of those makes if difficult. But I think it has more to do with the boring issues… because they love the Hulk and they love Mark as much as I do.”
On Why A Planet Hulk Film Might Not Work:
“It [Planet Hulk] absolutely could be put onscreen. I don’t know if it should. I think part of what makes the Hulk great is the world around him and the Banner of it. And it would be mad expensive as well. I think if they were going to do a Hulk movie, they’d want to keep it more grounded.”