The way the rules work, a private foundation has to spend 5% of its capital on its intended purpose. Thing is, that 5% can include "administration" costs like paying salaries and benefits for the family. They really need to raise this to 10%, minimum.
Art is a massive tax scam. You should only get a tax deduction on the purchase price (not "appraised value") and only to a public museum and there should be strict requirements as to what a "museum" is.
But it's really quite disgusting what lengths billionaires go to to avoid paying for the society that makes their wealth possible.