Human drivers pay one insurance, for themselves. It’s easier to swallow because most drivers think they are above average skill. Not so easy when they need to cover someone else’s coding mistakes. And if the company has to pay for every car that self drives that can get ugly fast, one bug and half the fleet has a fender bender.
Chances are they just self-insure (like they are now) and eventually will have some group insurance if they can actually prove it's safer over the next half decade.