For friction drive to work, there must be a considerable force to hold the wheels against each other. (the friction coefficient "mu" and the usually gravitational force, g) This produces big forces on the axles or hubs and the driveshafts. bearings will need to be super strong. But for a light car or a Robinson R25 (the beltless version) the effort might be worth it.
A gear will make the other gear turn with a minimum of force (other than the rotational torque) - just enough to stop the gears from moving apart.