"I don't have a pre-mapped view of the local mall, but I still manage to not run into anything."
In fairness, you do have some of the most sophisticated sensing, interpretation, positioning, path-finding and error-correction software imaginable, all running on hardware developed and refined in parallel over millions of years and exquisitely tuned to work together seamlessly. You also have access to a vast store of comparative information that works with unbelievably versatile pattern-matching software to identify all manner of objects in the environment, supplemented with an unequalled ability to infer the properties of objects by observation of their behaviour and vice-versa.
Further, the whole package is capable of near-spontaneous self-improvement and efficient learning routines which enable you to not only deal with new situations in suitable ways but also improve the efficiency of any subsequent approaches the similar problems.
There is nearly no engineering or software problem that can't be solved to get drones delivering packages - the issues becomes the ability to do so without spending many, many times more than the benefit gained.
As one poster said, above, the trick is to get the environment suited to the use. That is clearly not the case for this proposal so a better option would seem to be the continued development of self-driving cars. Once this is sufficiently advanced, efficient delivery vehicles could be designed.
That has many benefits, not least of which is that the investment is already there - both in the infrastructure (roads) and the technology. You also have a much broader range of packages that can be transported so your investment has broad use.
There is of course the problem of actually getting the package into the customer's hands but considering the issues presented in the article of the increasing density of populations and the types of dwellings we inhabit (i.e. apartments), this is no more problematic for a self-driving vehicle than a drone. As it will be near-impossible to take the parcel directly to the recipient, the recipient must meet the delivery part-way.
The only added concerns for a vehicle above a drone would be package selection and dispensation once at the destination and parking.