In chapter Sixteen of his bio, Cubby Broccoli tells us that Sean Connery "threw off what he saw as a straight-jacket and strode out in search of a new identity." Thus leaving James Bond for the first time, after completing YOU ONLY LIVE TWICE. "Sean had no contractual obligation to us, and in any event, I never fight to retain a reluctant performer." I believe I have read in other publications where Broccoli said they had released Connery from his obligation to make a sixth Bond movie, in the hope that it would appease the restless actor. I just came across a magazine article that shows there was likely a lot of legal action to arrange that release.
The January 1967 issue of Movie TV Secrets magazine features an article titled, SEAN CONNERY: I'M ONLY MARKING TIME. In the article, it says the following;
"Sean will soon be seen in his fifth Bond picture, YOU ONLY LIVE TWICE. And this could be his last stint as 007. At present, there are two sides to the conflict concerning the fate of James Bond and Sean Connery. On one side are the film execs who are fighting for one more Bond picture and they claim that they will make a sixth as per contractual agreements---with Sean starring, of course.
On the other side of the Bond controversy is Sean, who claims that this current film will be his last---that he and James Bond are parting company for good.
"Right now, I'm playing the waiting game," Sean admits. "There's a lot of red tape involved, but I think I'll get my way. It's not as if I were turning my back on the people who are responsible for my success. I think I've given enough of my career for the cause. Now I want out. I didn't want to do the last picture---but I did. I won't easily be convinced to do another. I figure I've got enough time left to prove myself as an actor and that's what I want most now."
According to inside sources, Sean will win this legal battle and the film execs will have to find a replacement for him should they decide to go ahead with plans for another Bond thriller.
Further down the article Connery says, "But I can't do anything till I'm rid of James Bond."
The article ends with;
"All this is in the future---right now, I'm just going to wait till I get my release from my 007 contract. When that time comes, that's when I'll really start to move. I don't suppose I'll ever lose James Bond, but from now on, he's coming along just for the ride. There won't be room for both of us in my life."
Now the source magazine was certainly not known for it's accuracy in reporting, but this article has a legitimate wording to it and I believe it reveals a small glimpse through the back door of the movie making world. Big money deals usually are not broken without a lot of lawyers.