Instead you have access to a fleet of specialized vehicles that are optimized for different tasks. Eg many trips might still be with only one or two passangers, and then a small two seater makes a lot of sense. If you need larger capacity you simple order a ride from a suitable vehicle class.

So building it without dead weight that will almost never be used makes sense.

If you're a bigger party, there will probably be bigger robotaxis to summon. Or take two cars.