For the same reasons that he spent more than 3 million to have all information about himself sealed. The same info that Romney said I'll show you mine if you show me yours. The same info that he never talks about and when brought up he quickly changes the topic or goes on the defensive. He has things that will tell a different story than what he has claimed. If he were a Republican the press would be ripping him a new one, and they'd push for impeachment. Just like Clinton, he lied repeatedly but he's a democrat, had it been Bush they would have crucified him. The press is left wing liberals, Obama can do no wrong as far as they're concerned--so the story never gets told- Obama is great, in their liberal BS world, he's hiding things that he doesn't want anyone to know about that's why he won't do it pure and simple
Because he has shown everything he needs to show and he is too adult to play trumps game. Trump is just looking for publicity and would either declare himself unsatisfied with whatever Obama did or he would just declare bankruptcy... Again.