"The problem with rich people is they don't spend their money"
They don't sit on piles of cash (i.e. literal bits of paper) - they own (purchase) assets of various kinds and even if they do have large quantities of cash sitting in a bank then this is put to work by the bank.
I should be clearer with what I mean; the problem with rich people is that, relatively speaking, they don't spend their money. Poor people spend all their money, fast. Rich people seem to have a lot of money tied up in swapping things with each other (for exmaple, stocks, which are not investments in the company except for the first time they're bought).
If there wasn't a downstream speculative market in shares then the value they would get when sold initially would presumably be far less so the companies or individuals getting the money at that stage would be worse off.
It's not inherently a problem; it's relatively a problem, given that swapping shares around each other creates no value (i.e. nothing of use to the world has been created), but the rich could instead blow it all on actually creating something or rather, paying for people to do work that leaves the world more actually wealthy (by which I mean, not "has more money" but "has more value"; Bill Gates stumping up cash to help wipe out Polio will leave the world phenomenally more wealthy, but with the same amount of once-owned-by-Bill-Gates cash in it - this is an extreme example of how to do it, but with the very rich it has to be extreme, because unlike poor people, the very rich simply can't spend a significant amount of their money feeding themselves and having a room redecorated and going to the movies).
Also, would it really be so bad if the stockmarket was less speculative and the benefit from owning stock was expected to come in the form of dividends? Everyone would have an incentive to make companies reliably, long-term profitable instead of prone to boom and bust.
Edit to answer the below: Yes, that cash does come from some very wealthy individuals, and what they're doing there is paying for people to do work that leaves the world more actually wealthy (hopefully - if the business crashes and burns when it turns out the world doesn't want shoes that are also electric bananas no new wealth was created). They're hoping to get a lot of that new wealth for themselves, true, but lots of it goes elsewhere too. They're not just swapping shares around; they're actually paying people to do things.
They don't sit on piles of cash (i.e. literal bits of paper) - they own (purchase) assets of various kinds and even if they do have large quantities of cash sitting in a bank then this is put to work by the bank.