You are confusing 6k and 12k mortgages: the former is to buy a modest house today in most decent areas in the US. The latter is to buy a modest house in Bay Area, where a large fraction of hacker news users reside.

A “modest” house to me is a median house: around 2k sqft, run-of-the-mill construction, cheap materials, 8 feet ceilings, <10k sqft lot.

This is the reality in good parts of US.