Except then dynamic dispatch won't be fast enough, so they or a competitor will have a fleet of self driving cars driving around 24/7 most of the time empty so

Except then dynamic dispatch won't be fast enough, so they or a competitor will have a fleet of self driving cars driving around 24/7 most of the time empty so that there is always a nearby car ready. The kind of market "efficiency" seen in the housing market where huge amount of property is left empty.