It's because he doesn't give a shit, because he doesn't actually believe other people exist.
In his experience he can simply bully people around him into telling him that yes, Mr. Trump, you are the hero. As we see.
As for actually helping people, I truly don't think he even understands the concept.
Whether the remedies he proclaims are real or not don't matter a bit to him, even slightly.
It's all about him in the moment.
Listening to experts means admitting he's not the expert already, which to him is an impossibility, as only he exists.