Is it the desperation of people who need the money so badly they will constantly cheat the system? Can you design for that?

I don't think the motivation on the part of the drivers who do this is very important. They're intentionally deceiving Uber customers, and in some cases endangering them. That just has to stop, even if the driver is desperate. The point here is that it's Uber's responsibility to stop it happening, and Uber has apparently chosen not to (like you, it's not that hard). That will be very hard to justify, especially as Uber were running TV ads about how they do background checks on all their drivers here in the UK recently.