(1) Americans consider housing to be an investment. An investment is only an investment if you expect a positive return over time. We generally want that investment to match or exceed inflation.
(2) That's antithetical to the idea of affordable housing. It's either affordable or an expensive, appreciating asset. It literally cannot be both at the same time. The only reason it's worked thus far is the broad-based expansion of the US economy and of specific population centers like SF has masked the problem for many, many years. Especially in conjunction with 30-year mortgages requiring 2% down. That's some serious leverage.
We don't talk about the lack of affordable AAPL shares do we? That's insane, it's an investment, we want it to go up. The less affordable, the better!
(3) Renters tend to be younger, transient and not vote. Owners tend to be older, wealthier, have deep roots in the community, and vote their asses off. They also aren't huge fans of change. They vote their interests: whatever keeps their, on average, largest investment performing well.
If you want cheap housing forget rent control. Allow developers to build up as high as the infrastructure can sustain. Allow smaller units, too, micro-apartments like whatever that place is on Mission, Panoramic. It's time to re-think the idea of housing as an "investment." We need to re-focus the narrative to make housing much more utilitarian.
This is reflected in major housing markets around the world, like Tokyo. They don't consider housing an investment, and they have some of the most affordable housing in any major metro in the world. [1]
[1] https://www.vox.com/2016/8/8/12390048/san-francisco-housing-...