Technically they don't hoard the cash, they loan it out to other rich people with the expectation of a return on their investment. Or theyhoarfd property.
Its not even the loaning out of the cash that is the problem. The real problem is that they spend the cash on ways to prevent other people from having the opportunity they had. This goes for political routes, such as donations to influence tax breaks, goverment backed monopoly, etc. Its also spent buying competitors or losing money to crush conpetition.