Housing bubbles are caused by the average wage of poor to middle class income brackets declining over time.

Lower wages lead to less homes and real estate being bought. This leads to the average value of real estate declining on reduced demand due to less consumers being able to afford them.

It might be fair to say: housing bubbles are symptomatic of wealth inequality/wage inequality. All of the wage increases which were supposed to go to poor to middle income earners instead went to CEO's. This wealth and wage inequality weakens the economy and creates negative effects such as: housing bubbles.

There are a few different perspectives to the housing issue. The media seldom covers any of the relevent ones.