Vacuum insulation doesn't weigh a whole lot, you could hold the pizza in an insulated cargo bay.
It's all an interesting engineering problem, you'd probably need a separate set of small ducted fans (inefficient, but safe) on the part holding the box so you could keep it steady in high winds as you winch it down. I think in urban environments and if you make enough drones it might work technically and economically if no patent vultures shut you down (might as well not try for at least a decade).
The drone will eventually kill someone though, just like pizza delivery drivers kill people. Not sure if people will accept it from a drone though, we're more forgiving of human failure than technical malfunction.