One factor that wasn't mentioned here (probably because people don't really mention it publicly) that I've anecdotally heard of from a number of people in tech who've made the SF->NYC move is the better gender and career diversity there. For men this can equate to a better dating lifestyle, and just in general some want to be surrounded by people besides tech bros.
Regarding politics, I wonder if another way to interpret this is people who find San Francisco too liberal (or unsupportive of Trump) and want to move somewhere more representative of how a majority of the country (however you define that) thinks.
Regarding politics, I wonder if another way to interpret this is people who find San Francisco too liberal (or unsupportive of Trump) and want to move somewhere more representative of how a majority of the country (however you define that) thinks.