There's only a limited amount of time one has. The private jet is to save time (convenience). In one of his interviews he talks about how he is always solving problems and his brain is running a million miles a minute. His brain is wired differently than most people. He has so many ideas running through his head. He doesn't have time to work on them all.

He doesn't have many expensive tastes. He doesn't live a life of luxury, he's not covered from head to toe in brand name clothes. He doesn't own a private island. He could care less about that stuff. Yes he has a huge ego but rightfully so. Look at all that he has accomplished against incredible odds (Tesla and SpaceX almost failing).

I do think he is genuinely trying to expand the realm of human consciousness and save the planet and create a backup plan for humans (colonizing Mars). Overall I think he is a net positive for mankind.

If anyone really thinks he is doing all this just to get rich needs to do some more research on him.