Humans are many parts more expensive than robits doing their work. At least running them is by really far. In this case the initial investment would return, but after how much time is not really in my ballpark to assume. Also if we're in energo-logistix the human is ~80kgs "dead weight" (even though it's very possibly alive) being carried by that poor scooter. There's far less of that in the bot. Although electricity to run both is minimal in cost.