I'm not sure Thomas is even very comfortable with his own party (even neglecting the obvious disconnect between law and politics). He strikes me as rather alienated across the board.

But I find it hard to imagine that anyone who cared about the law and had made a career on it would want to resign from something like the Supreme Court simply on the basis that things had become a bit too stressful or the passion had gone out of it. That's not just a job, that's a vocation. And you don't stop doing it just because you don't have a spring in your step all the time.