Except the supply here is necessarily constrained by the amount of land available to build on. You're treating this like microeconomics 101, which is a fundamentally flawed way to look at the problem.
Nearly 75% of land in San Francisco alone is zoned for low density single-family or duplex homes. 37% of it is just for single-family homes alone. [1]
Nearly 98%(!!) of land in San Jose is zoned for single-family homes. [2]
Replacing every ~10 single family homes with even a 6-7 story apartment building can easily increase the supply necessary to reach equilibrium, and that's ignoring the fact that you can build affordable apartments that are >20 stories (see: Long Island City, New York).
Nearly 98%(!!) of land in San Jose is zoned for single-family homes
You misquote your source (it says that NYT says that it is 94%, but that's hogwash given that far less than that is zoned for any form of housing). The referenced NYT article doesn't annotate a source.
More likely, the data says that 94% of precincts have at least one single family home.
Well over 10% of land is rights of way (e.g. streets, watersheds, etc.), easements, or is public property.
The link seems to indicate 94% of residential land in San Jose is zoned for SFH.
But even that could be misleading, since San Jose has massive city boundaries that includes hills and other places that really couldn't be built on regardless of what they were zoned for.
This is true, but zoning laws are ultimately determined by who owns land. Landlords and landowners are incentivized to increase the value of their property at the expense of everyone else. They use zoning laws to do this, which they indirectly control by being active in political lobbying.
Why would they sell a house they enjoy living in, near the school their kids attend, near the jobs they work at, in the city where their friend are? Or do you propose to force them out?
Because if that land was able to be developed into MDUs, the value of the land would be so high that you'd be a fool to not take it.
For example, here in Chicago the value of land downtown is upwards of $40 million per acre. It has nothing to do with the location of the land or that we're completely maxed out for development. It has everything to do with the fact that you can build 250+ units on that plot of land.
Why would you build 250+ units on a plot of land? Because people would want to buy or rent it. Why would people want to buy or rent it? Because the location is good.
I think you misunderstand my position. Nobody is proposing proscribing single family homes, or forcing people out of their homes.
People will sell their homes in the market, as they do today. Today it is illegal for a buyer of such homes to build multi-story apartment buildings in their place. The argument is to simply allow such construction to happen.
And I am explaining to you why those 10 families will vote against any of your proposals. Because once you allow more building the next logical step is to force them out to make some money for developers who'll wreck their houses and build those condos.
Nearly 75% of land in San Francisco alone is zoned for low density single-family or duplex homes. 37% of it is just for single-family homes alone. [1]
Nearly 98%(!!) of land in San Jose is zoned for single-family homes. [2]
Replacing every ~10 single family homes with even a 6-7 story apartment building can easily increase the supply necessary to reach equilibrium, and that's ignoring the fact that you can build affordable apartments that are >20 stories (see: Long Island City, New York).
[1] https://www.latimes.com/politics/la-pol-ca-single-family-zon...
[2] https://haasinstitute.berkeley.edu/single-family-zoning-san-...