I mean, they can't personally use those billions on themselves, so the family is still less wealthy for it. Sure it still gives them political power, but personally, I'd rather have the money than the power. So it's quite possible they do plan on doing good with it. And whoever gets the trust after them still will be required to use it in a relatively narrower way as opposed to the family just buying another house or something.
So it's true to be skeptical, but I don't know if I'd argue it's purely setup to shelter money since it doesn't really shelter money. Its like putting money in an FSA to avoid taxes. Sure, you avoid taxes, but you can only spend it on medical supplies. Is it really sheltering at that point? Honestly, it's kind of sad that the FSA is only example I can think of that most people could theoretically relate to. Billionaires just live in a different reality.