in my opinion, bad neighborhoods have a large amount of cell phone stores because the people in the bad neighborhood usually don't come across (or have for that matter) phones. And to see the 'cool' cellphones in person and to have the people sell it in person, the people in the bad neighborhood should want it more. And considering the modern generation we are living in right now, people like technology and want it, in the term 'humans as economical creatures', a human's want will never be satisfied, they will always want more. So, as I said, people and their families like technology, and all the cellphone sellers will come to the neighborhoods who will buy and want more, why would they sell in places where people already have cell phones, so they go to bad neighborhoods.
unless you mean 'bad' isn't 'not highly rich' then I don't know, but as a thirteen year old, I tried.