If you look at the surface area of the world, a tiny percentage of it is taken up by people's heads. Like, probably <.01%. Unless you'r eat a large gathering (where right now it's illegal to fly drones.)
It's not just people's heads that need protection. Roads, traffic lights, cars, power lines, windows... people can die in lots of ways other than having a drone fall directly on their head.
If you look at the surface area of the world serviced by Amazon delivery and population densities there, chances it hits someone's head are pretty decent.