"Crime" is not at the core of this change. You'd know those things if you lived here, but you don't. You're just repeating what you read in the WSJ opinion section.
It's more like crazy high rent, bad transit, generational disillusion with traditional NY careers like finance and law, the advent of "feasible" remote work and, I wanna say, the effect of social media making it clear you could be somewhere where it's usually warmer, happier, healthier, and more human.
Speaking as a former Manhattan resident for 7 years who moved to Miami this Summer
It has everything to do with expensive housing. NYC is becoming wealthier and whiter, with low income and minority residents forced to move out over housing costs.
It's tough to say, but seems like the defund the police movement "locked in" a lot of the damage caused by COVID and continues to exacerbate it. Rule #1 of getting out of a bad situation is to stop making it worse.
Also, the 70s and 80s were peak times for young men who grew up with leaded gas poisoning. Previous generations did not have as much car pollution, car usage increased which led to those increases in crime.
Perhaps quality of life is part of the equation but your comment tells us more about your preconceptions than about the reality of the situation.
Crime is down year on year.
https://www.nyc.gov/site/nypd/news/p00095/nypd-citywide-crim...
The article also lists the reason. The huge rise in cost of living and housing.