I think Trump may have started out with the plan to run for the publicity and to promote his brand but at this point I think he really wants to win the presidency. At this point in his life he has enough money that an extra couple billion won't do much to change his lifestyle or legacy.
But if he were to become president, he would be only the 44th person to be president, would have a definite mark on history, etc. For someone who puts his name up on the buildings he builds, I think the legacy and fame aspect of the presidency would be more attractive that whatever money he would make by forgoing the presidency and continuing in business.
Edit: There have been 44 presidencies, 43 presidents
But if he were to become president, he would be only the 44th person to be president, would have a definite mark on history, etc. For someone who puts his name up on the buildings he builds, I think the legacy and fame aspect of the presidency would be more attractive that whatever money he would make by forgoing the presidency and continuing in business.
Edit: There have been 44 presidencies, 43 presidents