That doesn’t necessarily create jobs or trickle down. If billionaire A buys stock in billionaire B’s company that provides an automated web service, money may change hands but the workers may not see any difference in salary. Maybe they need to spin up a few additional cloud instances to handle a new business area, but that won’t meaningfully impact Amazon’s workload.
Or suppose they buy a painting from another billionaire for $20 million - did that really create any jobs or middle-class wealth?