As best as I've been able to tell, it was a mixture of:
An increasingly narrow social circle of people willing and able to disagree with him.
An increasingly large social circle of people willing to tell him what he wants to hear, and willing to try and shape his world view.
And drugs.
He has sadly reached the stage where he is unwilling to have anyone around him who will openly disagree with him. Doing so is a firing offense.
He has absolutely reached the point wealth wise where it is impossible to make new friends who you can trust to not have a motive in every interaction with you.
And he has, without question, become someone that decent people from his past likely wouldn't want to be around.
I'm not sure that it's going to be possible for someone in his current position to reform without losing the vast majority of his fortune first. And even then, I'm not nearly as optimistic as I could be.