I agree its a recent phenomenon but it's not just the virus. I was born in raised in the city. I remember the bad old days. I see what's happening with the far left and their want to gut the NYPD and I foresee it backsliding into the bad old days. Crime is already ticking up but it's too early to point at that and say it's happening. It's a longer term projection I am making.

Probably more like 20 years. Boston, for example, was still losing population until the late 90s. (And the last major tech employer at the time also left during the 90s.)

Demographically, you were mostly seeing college-educated young people make up the net inflow over the past 20 years. I suspect that layered over the virus effects, you probably had some demographics who were on the edge of moving anyway--which is one reason that so many of them pulled the trigger fairly quickly.