Quadcopters scale up fine, in fact as other commenters have mentioned they get more efficient as they get larger. However, quadcopters are mainly useful becaus

Quadcopters scale up fine, in fact as other commenters have mentioned they get more efficient as they get larger. However, quadcopters are mainly useful because they are simple and cheap. Once you add the amount of redundancy necessary to safely carry a human (I am not convinced they have hit that bar here) it's no longer cheap, and it makes sense to spend a bit more on a helicopter, which is much more efficient.