Here are some articles discussing the current economic state of housing construction and affordability.  They might explain it better than I am able to.

Great article and video on how land, labor, materials and regulation have eliminated construction of starter homes.
https://www.cnbc.com/2016/05/18/for-homebuilders-new-regulations-mean-no-new-starter-homes.html
"these regulations, all they are doing is making sure the little guy doesn't live near the big guy."
"rich people and the dessert grouse are protected"
"they [regulations] are keeping first-time home buyers out"

https://www.cnbc.com/2017/08/24/there-are-no-more-low-priced-homes.html

Calif. Legislatures own bipartisan analysis identifying undersupply as a primary reason for housing unaffordability.
http://www.lao.ca.gov/reports/2015/finance/housing-costs/housing-costs.pdf