Uber traditionally operates on the service-included model. That was very well established before some drivers agitated for a change. Since then, Uber has adopted an inconsistent policy [https://help.uber.com/h/f7385bf5-1748-4fd0-a57f-3d9b62facc45]. In this condition, I don't believe users have any moral obligation to tip. Drivers should also have very wide expectations about whether or how much tip they will receive.
If drivers are unhappy with their Uber comp, they can drive for Lyft or on their own account or whatever. There is no need for riders to condescend to intervene in these labor disputes by bestowing tips, and in fact doing so may encourage the kind of abuse that inevitably follows the establishment of customary tipping (minimum wage exemptions and pressure for laborers to evade taxes).