It's not so much that they're bored, although that's probably how they frame it to themselves.

For some people, it's that to be that rich you have to ignore a lot of suffering and inequality. I think that takes a toll on your mental health if you don't constantly distract yourself, hence all the thrill-seeking/chaotic behavior and drug use.

For other people, it's that after having a lifetime of no one ever denying them anything, or facing any consequences, they genuinely start to think they can truly do [whatever] they want.