But that's largely a sunk cost that (in SF anyway) has already been spent, right? It's not like that cost goes up on a per-ride basis.

For places where that's already done, you only need to account for the cost of sensors/compute/maintenance of the vehicle themselves, which seem (intuitively) like they would be lower than the expense to users. Which would mean that a ride is net positive.

Maybe it's the case that configuring and maintaining the cars is incredibly expensive. That would be the only way I could envision actually losing money on a "per ride" basis.