A lot of housing policy happens at the state level, so the fact that a large part of the SF voting population are renters can get cancelled out by the fact that home ownership rates are higher outside the city, at least in state issues.

Yes, but the political system is often more likely to represent the interests of the donors rather than the voters, and the homeowners are the wealthy class who can afford to buy votes and hold political sway.

It often doesn't matter who the renting class votes for, and politicians who represent their interests are less likely to collect campaign donations, which affects their likelihood of holding office

If votes can be bought, it's because people selling their vote don't really care about the issue.