You're applying double standards here. If Expedia is not an airline, then Uber and Lyft aren't taxi companies. Uber and Lyft buy the services of independent drivers and resells them to customers. If the ultimate commercial relationship is between you and the hotel or airline when you book through Expedia, then it's just as fair to say that the ultimate commercial relationship is between the passenger and Uber/Lyft driver. Just like how Expedia's role is connect a customer with an airline and handle the payment transaction, Uber/Lyft's role is to connect a passenger with a driver and handle the payment transaction.
Crucially, your statement that the commercial relationship only exists through Uber is patently false. Drivers can, and do, driver for different ride sharing companies. A passenger could hire a driver through Uber on one day, and hire the same driver through Lyft on the next.