He could leave at any moment, even with contracts. Hell “Best of Both Worlds” literally had Patrick Stewart and Jonathan Frakes in the middle of contract negotiations - either one could have walked away at that moment and the story was ready for that. (Picard obviously, would have been consumed, Ryker was offered his own command).
It’s a bit condescending to say that we should pity him because of TNG. He’s said multiple times that while his initial reaction was what you said, he’s enjoyed it from there on.
The vast, vast majority of people don’t get jobs and think “Okay here is where my career is going”, they are along for the ride. Many, if not most people find that they enjoy other careers more than others and swap, and there’s nothing wrong with that.
Don’t pity a man because he found something he loved doing and kept doing it, we should celebrate that.
