It's because the east coast was settled earlier, so a lot of the earlier small board or brick houses fell into ruins earlier. Also, eastern cities were largely industrial, and became not only the intake for immigrants earlier, but also for post-Civil Rights southerners coming north for work.
See post 78.
I understand that, however the criminals who inhabit those big cities are a huge part of the problem.
That's how we got ghettos here on the west coast. During WWII, blacks came west for work from the southeast because whites became soldiers, Japanese-Americans went to concentration camps. Blacks got housing near shipyards (Hunters Point shipyard in SF, Richmond ship-building, Alameda docks, etc.). All those places got ghettos, although the Hunters Point area in San Francisco has seen an influx of asians as blacks have left, and the area is improving.