Is it simply normal supply and demand? They had massive surge of prices that made construction more profitable so after a time lag, building boom happened, bringing prices back to the average long-term trend. If some place becomes 'affordable', its economy suffers because good people don't like living in places where housing is affordable - they move out.

Hey, here's a good way to improve 'housing affordability' locally: dumb down schools. People with cash will move out and prices will fall. Something suggests me it's not the solution really lol.

Affordability is relative. System always balances itself on the level that barely over 50% of people can afford housing (because it's a democracy). There's no fixing to it unless one abolishes either democracy (so no one cares what people want and developers have a free roll building as much as they want), or market economy (when the Party provides housing as it pleases).