Why are there roaches in some parts of Philadelphia and not in others?

Question:I live in Philadelphia. The section of Philadelphia that I live in is quite nice and has less than a 1% unoccupied dwelling rate. In sections of the city that are filthy, crime and drug infested have a much higher unoccupied dwelling rate and everyone has tons of roaches. Are roaches attracted to unoccupied dwellings? I have never seen a roach in my life and no one in my neighborhood has either. The streets in the roach infested parts of the city are littered with trash, but I am sure they keep their houses clean - so why would they have roaches? Are they attracked to the filth that lines the streets? Do they simply like the smell of crack? What damage do roaches do to a home? Do they carry disease? Are they attracted to trash or is it coincidence? Since the neighborhood that I am referring to consists of row homes, would it only take one dirty house on the block to have the whole block infested?

Answers:
Sometimes roaches like to move around to find places for shelter and food xD So maybe they like the smell of the dirty stuff and thinks it's someting to eat like rotting banana or egg xD
Roaches don't really do damages that much except they do smell weird and sometimes they steal your food or take a bite out of it xD And they are nasty ___Some carry germs and viruses but most of them won't kill you ___and they are attracted to trash because trash has lots of food related things inside_____and mostly one dirty house on the block can make the roaches think that all the houses are like that so they check every house or just the houses next to it xD