As others have noted the types of services vary widely by region and jurisdiction. Some have exclusive contracts with a single hauler to provide residential and commercial collection. Some have their own gov owned/operated fleet. Some contract for residential and let commercial have an open market.
The wild variety of situations means that large companies don't want to have to wade through all the possibilities at each of their locations and instead hire a broker to manage their waste at all sites. The broker then works out how to get them service everywhere and uses their domain knowledge to get a decent price from the hauler where negotiation is possible.
It appears to me that these guys are a Broker++ since they are building meaningful relationships with the haulers that service their customers. As they say in the article they have two customers (the waste producer, and the waste hauler). This is definitely a departure from the typical broker that treat the haulers poorly (delaying payments, short paying, never paying, ridiculous requirements, etc for the haulers). I can see it working out really well for them if haulers are comfortable letting this company inject themselves into their trucks via an app.
FYI - I work in the industry writing software for independent waste haulers. Before that I operated my family's waste hauling operation in CA. We offered 1x week residential and up to 6x per week commercial collection as part of an exclusive contract with the City. Our customers paid us directly but that's not always the case with city contracts.