If memory serves Abrams claimed he was "too much of a fan" to take on the film when it was initially offered. Not to mention the fact that he pointed out his "loyalty" to Star Trek. Than shortly thereafter he is officially named TFA director. It's obvious that it was about financial compensation. JJ Abrams apparent loyalty to his iteration of Star Trek clearly was not going to sway him from the potentially highest payday of his career. Even if it sucks, it's a win/win for him because the money will keep him secure and he would be welcomed back to Star Trek regardless of success or failure with The Force Awakens.