Since you mention Uber, I can definitely see in my city how the quality of cars decreased and they started using almost inclusively cheap immigrants who realistically couldn't pass a drivers exam in my country and have on multiple occasions driven into wrong directions/ran red lights etc.
Also, Waymo isn't even Google. You might accuse me of overstating this, but truthfully they operate as a different company.
There are schemes where undocumented immigrants ask someone to activate their account on their behalf. In practice, the person giving you a ride could be literally anyone.
Don't they? Allowing messier, older, and less pleasant cars would increase the supply of drivers, allowing Uber to place lower bids on those drivers, lower their prices, increase volume and revenue, and increase profit.
Sometimes it's worth not worrying about problems too far in advance.