It wasn't quite as simple as that. From what I remember, the rights to Watchmen were supposed to revert to him after the book went out of print. But DC just kept the book in print forever, denying Moore any say in what was done. Keep in mind this wasn't normally done at the time, it was a pretty underhanded move they pulled, especially after Moore did so much good work for them (Swamp Thing, Green Lantern, the Phantom Stranger, etc.).
They screwed him, make no doubt.
It's an older meme, sir, but it still checks out.
https://knowyourmeme.com/sensitive/memes/ate-my-balls