And are doing it out of their own pocket. Uber isn't paying them to clean unless someone pukes in the car, and they certainly don't get anything to cover wear and tear and maintenance. However, drivers need to maintain a clean vehicle or else they get a poor rating and are forced out of the system, and need to maintain a working vehicle or else they cannot work that day. When you start to factor that in, your rate as a driver sinks like a stone.
If someone bought the car exclusively for Uber, the math would've been simple. But people run their own personal errands, drive for Lyft, deliver for Doordash or Instacart, etc.
There's been an [older] thesis that in a nutshell, unless one happens to chase the surge, driving for Uber/Lyft/Grab is a money-losing proposition.
and incur new costs of buying, maintaining, parking and cleaning the vehicles