Most cars are not used by people living out in nowhere, on a road that only two people use.

We could run a smaller vehicle if there are only ever two riders that need the service, or avoid having a route when there are too few people.

School districts can sort out how to move small numbers of children spread out in rural areas, the same can be done for any population. It also means that there might be some area that don't have enough mass for mass transit.

But right now we have a lot of places with plenty of mass that just refuse to believe that mass transit can be a solution because of decades of car company propaganda.