The article mentions that many of these companies are effectively WaaS companies, though they're called "third-party logistics contractors, a.k.a. 3PLs".
From the article: "These companies often fulfill orders for more than one retailer out of a single warehouse. America's largest 3PL, Exel, has 86 million square feet of warehouse in North America..."
DHL and UPS, among others, offers this service.