the problem is that you still need a driver, so frequency is going to be limited, which makes the service barely usable. Lack of places for vehicles to pass also limits possible frequency on these rural lines.
the idea behind monocab is that you can just throw more vehicles at the problem, so people can either just order a cab or you can have them constantly circulating like a very strange merry-go-round.
Railbuses are still good, but they made a lot more sense in the past. These days people have very very little tolerance for waiting.
unfortunately the same effect isn't achieved when people just take the headset off and go to bed in their own home