The quick answer as to why NYC and most northern industrial cities were twofold>>>>
#1 White Flight in the decade after school busing and integration, the white middle class fled to the suburbs taking their tax dollars and small businesses with them.
#2 The 1971 Arab Oil Embargo and OPEC price hikes made to expensive to manufacture in the hundred year old northern factories. These buildings were fine when oil was 5 cents per gallon, not $1.00 or more
The rust belt was created and the south rode a new industrial wave to economic superiority. Others just oved their factories offshore.
I was involved in a major sewing manufacturer’s business in Waterbury, CT. We could not afford to heat our 1880s buildings. We moved all production to South Carolina. The buildings were let go for taxes. They remained vacant for more than 30 years