But as people leave those expensive cities, won't they become more affordable? I mean, they are expensive because there are more people than available housing,

But as people leave those expensive cities, won't they become more affordable? I mean, they are expensive because there are more people than available housing, and because there are lots of people making lots of money so they can spend more on stuff. But if those people want to leave, that reduces demand so prices should reduce. Eventually, we should reach an equilibrium (or at least something more stable).