Drones face various problems originating from general avionic and technical/physical limitations, their purpose, material resources, interaction with humans, and energy. Beside all that there are economical strings attached. For example, it might be feasible to deliver packages via copter to the front door of people living in those US suburbs where everyone has a lawn, a car or two, and the roads are wide. However, such living conditions are not the most prominent ones on earth. In Europe people live in much denser populated areas. While there are some areas where you have single houses these areas are small and often mixed in with other housing structures for more than one family sharing the same exit. Even more large parts of European cities are filled with building structures with 4-8 floors with many parties living in the same house or compound. If you visit Beijing or any other Chinese city you can observe that people live in large compounds with 30 or more story buildings. While in Europe you could at least speculate about opening a window, you cannot do that in such buildings. And in China you should not open the window if you are not interested in lung problems. So parcel delivery does not work very well in most areas. It also does not work when I am not at home. However, what works is delivering it to my workplace by humans (drones cannot fly in we cannot open windows).
If you allow copters and humans interact then you have to make sure that there is enough distance between copter and human even for emergency situations. All of this makes parcel copters not to be very likely to become a dominant transportation tool.
Another use case are surveillance copters for police and media. They are already in use. However, they are only then cheaper than non flying cameras when you do not have too many of them.
Each drone requires energy and must be recharged or refueled regularly. All that energy must come from somewhere. If this is more carbon based fuel, we will have increased pollution in cities. We try to get rid of that presently so that will most likely be limited or forbidden. Leaving H2 or electricity (E). H2 requires a lot of energy to be produced and same applies to electricity. However, H2 allow longer flying time while the fuel is more expensive then electricity. Anyway, energy cost is a relevant factor. For a town of 250 000 inhabitants you have 100 roads (densely populated area) with lets say they are layed out like a checkers board (true that does not really fit any town or city in Europe, but who cares). That gives you 104 persons per tile, which would be not enough for where I live, but anyway. Each tile is 200 x 200 m. Making the road length 9800 m. To completely cover the area a drone must fly up and down that approx 10 km. Lets assume that this is done in 20 km/h (median bicycle speed) a complete sweep requires 30 min (29.4). As a typical robbery requires only several minutes, lets say 5, you need 6 drones to get that amount of coverage. That means you need 600 drones and most likely another 600 at the recharger. I do not know what these drones police uses at demonstrations cost, but police equipment is always extra expensive, so 10000 EUR/$ would be an assumable price. 12 000 000 EUR/$ + maintenance + training. Too expensive for the police. Especially, more expensive than just a view officers which could do the same on a bicycle.