Thank Wall Street, Rudy Giuliani, and gentrification. While the pictures from the 1980s seem desolate, the population of Brooklyn was not that much less in the mid 1980s when these pictures were taken: https://www.bing.com/images/search?view=detailV2&ccid=ScGoR6.... There were people there, they were just too poor to support a robust ecosystem of gyms, cafes, and restaurants. The growth of finance and its satellite industries provided the money to support satellite businesses like restaurants and cafes. Meanwhile, in the mid-1980s, the city was overrun with crime. In 1985, there was a mob hit at 5:30 pm on 46th and 3rd in Midtown, outside a popular steakhouse. The area looks like this today: https://www.bing.com/images/search?view=detailV2&ccid=ScGoR6.... Guiliani's aggressive prosecution efforts decimated the mob in the city.

That's the unfortunate mechanics of a society where there has been no income growth for the bottom half in decades. If a place was sketchy before and now it's nice, it's because yuppies moved in and pushed the previous residents out. In Brooklyn the percentage of low-income residents plummeted from 45% to 15%, while the percentage of upper-income residents jumped from 5% to 25%: https://www.nytimes.com/1982/09/20/nyregion/census-traces-ra....