Since 65-70% of SF residents are renters from what I can gather, how/why exactly do these laws keep passing that restrict housing and increase home prices and rent?
Renters vote less. Renters don't show up every week to city council meetings. Renters don't write objections to planning proposals.
They touch on this sort of indirectly, but homeowners aren't the only objectors. Often NIMBYs don't like development because they don't want to live next to a tall apartment building with lower income people, for example.
Because it's not very intuitive to most people that things like zoning, rent control, and laws against gentrification are anti-renter.