Taxis are usually disgusting too. I won't take a cab because I frequently feel like I need to shower after sitting in one. I rate Uber drivers almost exclusively by their cleanliness, which is usualy very good.
Taxis can be dirty, but there is nothing necessary forcing this state of affairs, and as you say at least one taxi company mantains a higher standard.
still, it is not clear that making the car self driving will make the taxi cleaner on average.