What is this, the 1970s? The Bronx? Guy, you can rent an entire house for half of what a studio in the crappiest neighborhood costs round here. It's also part of NYC, THE Capitalist Capital of Planet Earth, the economic driver of America, and the engine of the world.
As for those other places, like the Bx, NY, it was the departure of industry for the suburbs, the South, and to other countries that caused economic decline since the 1950s. That's called Capitalism, son.
Well, partly. Tax incentives and subsidies plus lower costs in everything from real estate, infrastructure, and amenities to wages enticed manufacture to move south and abroad. Do you know which party has from its inception fostered close ties with business?
Causality, it's a thing, AKA, which came first, the chicken or the fried egg. If Democrats were somehow the cause, why would these people vote for them? It wouldn't be like Republicans - who've also run things in these places just didn't care and that's waht voters saw?
btw, all of those cities have areas that vary in how economically sound or not they are, and all have witnessed revivals of some sort at least in some sections.
Meanwhile, what has the South done to turn its moribund economy in eternal downward spiral since the Civil War?