I discussed this with a very bright CFA Level 3 asset manager with $3B active and another $6B he advises on:

Rich people disproportionately hoard money and lock it up or invest it to make more - poor people spend what they make which is why they stay poor - but they need enough income to keep the consumer machine running.

When the rich don’t give the poor enough to spend, the system does not work and societal unrest is sure to follow.

Story as old as the guillotine.