He is putting that wealth to work by keeping it invested in his company instead of stuffing it under his mattress. That’s exactly how it’s supposed to work. That wealth is doing work for him and for the rest of the economy in the form of Amazon stock (setting aside various ethical qualms about Amazon). Stock is nothing more than an abstract representation of a slice of a company to allow for distributed ownership and for companies to raise capital. So instead of purchasing goods and services from a company, a shareholder provides raw capital to exchange for a slice of the company. That would make sense for a wealthier person who can only buy so many yachts and massages (goods and services), but it applies equally well to someone who is trying to sock some money away for retirement and have it grow over time.