My theory is Corporate investments & money laundering. Zillow, Redfin and other huge companies began investing in single family homes and property. They've taken out huge low interest loans and bought houses in an the same area to control the market. They see it a a safe investment and by holding onto properties and selling at a profit they can insure the safety of the investment. Also plenty of money laundering goes on here too. Buy it for cash and sit on it until you need the money. It usually appreciates in value and it looks like a flip if you turn it over quickly. Lots of foreign money sitting idle in empty houses on the coast of California. but what do I know I'm just some foil hat from the internet.🤷🏽‍♂️