> It's equally likely that people left because it's not worth it to commute to Manhattan everyday from those boroughs when the rent is so fucking high and the housing stock is so low.

I think its more like tons of office workers no longer have to commute to Manhattan every day so why bother living in expensive NYC when you can work from home in a quiet suburb with good schools and easy parking and cheaper houses. Then there's less need for stores and restaurants in Manhattan so the people in the outerboroughs who did work those jobs in Manhattan don't need to be here anymore either.