Great point by the other responder.
High level - Uber and Lyft have done a terrific job getting people to work for less than minimum wage. I've met quite a number of uberdrivers who work in Robotaxi-Ready cities (think Chandler, Tampa, etc) who work 12-16 hours/day, 6-7 days a week, and make $20k/yr after depreciation.
While sensors are getting cheaper, most teams respond by throwing more sensors on the vehicle. It seems unlikely there will be a <$20k robotaxi anytime soon.
TL;DR: Humans are cheaper than robots.