It's a basic principle of contract law that parties can't agree to a valid contract if they don't know the basic fundamental financial terms of the contract, like say,
the price.A driver does not know how much a passenger is paying for the ride. The passenger does not know how much the driver is receiving for the ride. Ergo, they cannot have formed a valid contract with each other. On the other hand, the passenger knows how much they are paying Uber, and the driver knows how much Uber is paying them. This indicates that the common relationship is Uber, and that the driver is acting as Uber's agent with respect to the driving services. This is supported by Uber/Lyft treating gross booking as their revenue. It is a long-standing principle of GAAP that if you are collecting money on someone else's behalf as their agent, it's not your revenue. If you are treating the money as your revenue, and their services as an expense, that indicates they are acting as an agent on your behalf with respect to the services/whatever that gave rise to the revenue. Because the driver is acting as Uber's agent, AB5 comes into play to determine whether they are an employee or independent contractor.
I don't know why you're fixated on Expedia. Expedia is a reseller, which is a thing that has existed as a legal construct for over a century and has an actual meaning and requirements defined by law. Expedia doesn't resell services, it sells reservations/tickets/etc provided by third parties that represent a right to a specific performance of a specified service at a specified time and place by that third party. Importantly, once a transaction is completed on Expedia, the customer must generally seek customer service from the third party, not Expedia, because Expedia's role in the transaction is completed, and Expedia only provides relief if the third party will not, and that relief is limited to refunding the customer for the amount they paid Expedia.
UberLyft don't sell services provided by third parties, they sell a service (transportation or food delivery), and it happens to be performed by third parties on UberLyft's behalf. In contrast to Expedia, none of the participants in the transportation or food delivery service get to select their putative counterpart to the transaction, or the financial terms of the transaction, and after the driver's part is concluded they usually have no further interaction with the passenger as customer service service issues are provided by UberLyft, not the driver. IOW, there are no hallmarks of a business relationship between the driver and customer.