It wasn't so much that.
From Timeout Sydney
Alan, why is it that films made from your comics never seem to do them justice? Is it a lack of intelligence or courage on the part of filmmakers?
It's not, it's simply because they weren't ever designed to be films. This is what I've been trying to explain to these stupid bastards for the past 20 years. They were designed to exploit all the things that comic books can do and that no other medium can. I wanted to give comics a special place when I was writing things like Watchmen. I wanted to show off just what the possibilities of the comic book medium were. And films are completely different. This assumption that if something works in one medium it will work as well or better in another, I've got no idea where that comes from.
Now, initially he was quite content with ignoring the films of his work while receiving his part of the creator's share. That changed with Fox settling out of court with Martin Poll and Larry Cohen over an unproduced script of theirs called Cast of Characters which they alleged was plagiarized and turned into The League of Extraordinary Gentlemen. Moore felt that the settlement by Fox was almost an admission of guilt. Since then, he's requested that his name be removed from all films of works that he doesn't own and that his share be sent to the artists. For the works that he does own that haven't been adapted into films, he refuses to sell the rights.