Level 4 (e.g. highways in good weather) is something that people buying cars will pay a significant amount for as an option in good weather. It does nothing for those who want robotaxis. But the former don't care about the latter.
You have multiple groups of drivers including those who appreciate self-driving assistance on long boring highway stretches and may not even drive in cities that much and those who never want to get behind a wheel or perhaps ever own a car.
Level 4 doesn't necessarily mean just highways - it could also easily include suburbs with well-designed roads that have been mapped in excruciating detail.
You could force the car to avoid certain intersections with lots of close calls, or give the car advance info about unexpected objects detected in the road by cars up ahead, etc. which would make the task a little easier.
You have multiple groups of drivers including those who appreciate self-driving assistance on long boring highway stretches and may not even drive in cities that much and those who never want to get behind a wheel or perhaps ever own a car.