For one, he has had quite a track record for entertaining the thought of running for president, but he always withdraws. It has been noted that often when he does, he has another project he really wants to draw attention to, such as a book, or in this case, a television series.
Secondly, he would have to disclose the nitty gritty of his finances if he were to run, and frankly, he is too much of a chicken to publicly release that information. He acts like he has a big set of balls, and might be someone who puts their money where their mouth is (after all, he was demanding documentation from Obama), but frankly, he's not. He talks big but he doesn't deliver.
Thirdly, even without a commitment to run for office, skeletons were coming out of his closet from his past. The problems his companies have had and the positions and public statements he made throughout his public career have already been coming to the surface and I am sure a long haul campaign would have been very damaging to his reputation.
Fourthly, he would have had to quit the Celebrity Apprentice, a show which is good for both his pocketbook and his exposure. A presidential campaign would cost him a lot more money in the long run, so it seems unlikely he will ever run.
And finally, the comedy... oh, the comedy. Donald Trump is not a man who can take a joke at his own expense, and with not only the current President ripping on him hard during the Correspondence Dinner, but the grim spectre of The Simpsons' predictions about the Trump Presidency after Lisa became the President would just hurt so bad.
Again, I quote:
Lisa: As you know, we've inherited quite a budget crunch from President Trump. How bad is it Secretary Van Houten?
Milhouse: [shows to a chart] We're broke.
Lisa: The country is broke? How can that be?
Milhouse: Well, remember when the last administration decided to invest in our nation's children? Big mistake.
Aide: The balanced breakfast program just created a generation of ultra-strong super-criminals.
Milhouse: And midnight basketball taught them to function without sleep.
He really was in a no win situation.