There's anecdotal evidence that drivers can "rent" a clean identity, meaning that the person who is driving the car is not the person that Uber has on record as being the driver. Uber not looking into this and not being pickier about it, fits with other "I know nothing" corporate behaviors.

And it's not like there aren't a plethora of relatively accessible technical solutions to fix this problem like looking for inconsistency in nearby devices that accompany the driver and the usage behavior metrics in use within the advertising industry to de-anonymize users. Figuring out who someone is when they don't want you to know it's them is a scarily well solved problem at this point... figuring out if someone isn't the same person you thought they were yesterday is comparatively trivial.