Three words:
Ego.
Ego.
Ego.
I think he loves the attention.
He’s Nucking Futz!
I would like to suggest three more words: money, money, money. Unless I am mistaken, donations accrued prior to an official declaration to run for POTUS can be used however desired. Sooo, if the old guy pockets a few million, it's his to use however he wants...