So why do the pilot in the first place? I don't think his movie career exactly took off afterwards. Also, IMDB shows that he "lowered himself" to make quite a few appearances in TV shows after the Trek pilot so why not one more appearance as Pike?
Look, I didn't know the man, I just know what I've read. According to
Inside Star Trek, p. 63, when they invited Hunter to a screening of the pilot in hopes of convincing him to do a second (since a second pilot was unprecedented and his contract therefore didn't have an option for one), his wife came in his stead, and after the screening she said (according to Herb Solow's recollection), "This is not the kind of show Jeff wants to do, and besides, it wouldn't be good for his career. Jeff Hunter is a movie star."
It certainly wouldn't be the first time that an actor has walked away from a TV gig in pursuit of movie stardom that failed to materialize. Just ask Maclean Stevenson, David Caruso, and Michelle Forbes. And whether it was about movies or not, apparently Hunter just decided after making "The Cage" that he wanted nothing to do with
Star Trek. Maybe he did the pilot for the money but decided he wasn't comfortable with the idea of being associated with a genre show. Maybe he didn't get along with Roddenberry. Who knows? The man's long dead. All we know is that one anecdote; the rest is conjecture. But it seems pretty clear that he just didn't want anything more to do with the show. He wouldn't even attend the screening of his own pilot.