One could also ask the same question of one Barry Soetoro. The answer is clear, nobody "volunteers" their history, it's up to the MSM to uncover their crappy history.
So the question that should be asked is WHY the MSM hasn't done their job?
Good point. It took a UK paper to go discover the fact that Bernie's kid is a bastard, something that was lied about by his campaigns for 30 years.