This seems naive. I'm sure the people looking for SROs or other low income choices are not the people buying $1M houses, but they probably have a good deal of o

This seems naive. I'm sure the people looking for SROs or other low income choices are not the people buying $1M houses, but they probably have a good deal of overlap with people who are buying houses that are at the lowest rung on the ladder, who themselves have overlap with the next cohort, etc. It's a market. Changing it in a major way at the bottom will have knock-on effects through the whole market. Of course, more directly, people with $1M houses might also be highly motivated to avoid "the wrong kind of person" being able to afford housing any where near them, their schools, etc.