"Anti-building regulations are the only meaningful reason why the housing supply is so restricted."

Prove your claim. The GP is right that there is essentially no undeveloped land in SF; a huge part of the housing moratorium debate centered on the fact that there are only a half-dozen or so vacant parcels in the Mission. This is true across the city.

You're arguing about underutilized land, which is a subject that cannot be addressed with simple assertions. In most cases, that "parking lot or burger king" is a contrived example that doesn't really exist: either the lot really is being developed (and you just don't know about it), or the owner of the land doesn't want to redevelop it (i.e. they're making more money with the current use than they would otherwise), or the land is in a place where a developer can't make a building work (pollution, neighborhood, etc.), or any number of other practical reasons.

I used to believe, like you, that "regulations" were the reason that SF has a housing problem. Then I started looking into it. Regulations make a difference on the margins, but the root cause of SF's housing crisis is simple economics: too much money chasing too little land. No matter what you do, it's going to be expensive.