Or more precisely, once a house attains some value beyond providing a roof over heads, the price of a house is no longer representative of a house, but a government backed asset that can never depreciate lest the pension funds fold.
A single house's price can easily go down. Even an entire city like Detroit MI can devalue. But those mortgage backed securities represent the national average.
With climate change the music may suddenly stop for flood prone areas like Miami once investors stop underwriting 30 year mortgages.
