I think some of the ultra-rich are just perverse. They like the idea that they are so filthy rich that they can somehow assign value to art through their money - and preserving a large part of their wealth by doing so, because once something has been sold for the X amount, a kind-of "market price" precedent has been set.

You can see this in meaningless art. You can even see it in ...SHIT:

https://en.wikipedia.org/wiki/Artist%27s_Shit

"In August 2016, at an art auction in Milan, one of the tins sold for a new world record of €275,000, including auction fees."

Yes, they can literally pump the price of shit and pretend it's art. They can even mock the mockery of the "art-is-shit" meaning, by giving extra value to the shit. We are talking about pretty high levels of perversion.