​Why is rent for private rooms in Bay Area so cheap ($500-750/mo)

[Tom Smith]

Why is rent for private rooms in Bay Area so cheap ($500-750/mo)?

I am looking through craigslist rooms & shares and many people are advertising private rooms for rent in Bay Area for $500-$700/mo. Why are the room rent prices so cheap? Are private room rental prices not as competitive due to high supply and lower demand?

These are rooms in extremely high housing price places such as San Jose, Palo Alto, Fremont, etc. 

I am looking at the Houston rental market too and the prices are basically the same for private room rentals $500-$700/mo.