besides spend it on frivolous shit like yachts and planes and stuff, there's no way it's all liquid. do they just park all their billions in a bunch of investment vehicles and wait for it to propagate itself? don't they get bored of just waiting and watching line go up?
This. If the peasantry are kept at a level where they have just enough to live, but not enough to see their children starving, they're not likely to rebel. And being rich enough to endow a huge network of clients and lackeys and mercenaries gives you agency to act in the world of big scary monsters. Having shitloads of wealth both keeps the underclasses in control and protects you from other rich people, rich people being the primary predators of rich people.