He sold the rights early in his career, in the 80s, before the shitshow adaptations started coming out. Once he realized the travesty they had made of his life's work, he vowed never to work with Hollywood ever again and even stopped accepting royalties, telling the studios to pass them on to the artists that had worked on the original comics instead.

Yeah, with the result that the only decent adaptation (V for Vendetta) doesn't have his name anywhere on it.