DC Comics declined to negotiate with Alan Moore over those rights and Moore chose not to work for DC Comics again – until they purchased the publisher who was publishing his comics, Wildstorm.
And a clause in the contract that maintained DC Comics in control of the ownership rights unless the comic went out of print, saw DC Comics choose to keep Watchmen in print in perpetuity, eventually making a movie. In a time when trade paperbacks in continuous print didn't exist.
Watchmen was published by DC Comics as a creator-owned project by Alan Moore and Dave Gibbons. Has DC Comics really gone there? I'll be reading at midnight on Tuesday to find out… but I think the controversy over this decision is going to explode again.