Because a lot of people actually like cities. Restaurants everywhere, clubs, concerts, etc. I figure, Manhattan will be a lot more affordable as well. My wife's company is HQ'd in NYC and a lot of the people that left are ready to go back already. They love the city, just hate the lockdowns.
I think you're going to both see cities not fully recover and also be a lot better for the people that want to live their because it won't be as expensive or crowded.
A lot of people, especially young people, live in teh city because it's a great lifestyle. Concerts, clubs, other people in a similar demographic just about no matter what demographic you want to come up with, lots of opportunities for niche interests, etc.
A lot of people are in the big cities for jobs, and can get most of what they want out of any small to medium sized city, and what they can't get (theatre, maybe
their professional sports teams, concerts with big name performers), they only take advantage of sporadically enough that they can get their fix on trips to bigger cities.
So I think the people that really love the city because it's a big city will stay and most of the money supporting the things they care about will stay (whether its from people living their or tourists), and the people that really just want amenities that can be found elsewhere will go elsewhere.
I think it will be a win/win, except a lot of large cities are poorly managed, and a lot of the people that leave are people that they need to pay exorbitant taxes. Not sure how that will play out.