it has to do with how a dollar circulates. I'm in pretty bad shape financially. I had 3 close family members get hit with major illnesses all at once. I'm still recovering and I'm not sure I ever will. What I'm saying is I spend just about ever dollar I get my hands on paying debt and buying food/shelter/transportation. There's a little discretionary funds in there for my kid. I try to let her do thing things her friends (who's parents didn't get economically cock punched non stop for 10 years) do.
Now take a Donald Trump. No matter how greedy he is there's only just so much he can buy. At some point his money is just sitting around, doing nothing. He'll invest some of it, lose some of it, etc. But He's only got so much time in the day to do that. Eventually it becomes a war chest laying around doing nothing.
When we take it even further, to the level the Waltons have achieved what we have is pretty much the dark ages. You've got a small group of folks with _all_ the wealth. They're more or less Gods (Divine Right of Kings, anyone?). They stop investing because, heh, why should they? They already have the best civilization has to offer. As a result things can really only get worse for them.
If the above sounds complicated it's because it is. That's what makes cutting the marginal tax rate so seductive. It sound like an easy answer to the world's problems. Supply side economics, right? But there really is a reason we called them Voodoo Economics...