Why are the high income couples living in apartments right now? Are there a large number of newly created high income jobs within the last 3-5 years? Or have those jobs been there all along, and perhaps even more high income jobs 5 years ago versus now?
As for the owners with low mortgage payments, not eveyone wants to be a real estate investor.
According to the San Jose Dept of Housing, average monthly rent is $1,269, and the median home price is $765k. Why on Earth would you ever buy with this disparity? No wonder there are high income households renting. Prices would have to come down at least 50% for many of those renters to consider buying.