it's not cheap at all and the privacy and logistical implications of letting a stranger inside your house is something not everyone wants to deal with. I would rather have a robot.
A human house cleaner by definition is a real human looking at your home every time.
Versus a small army of roomba's and equivalents mapping out floor plans and tangentially exposing human occupation times with that large data set almost certainly exposed to criminal and surveillance networks that will almost certainly use some of that choicer data to their advantage.
It's literally trade offs in both cases.