Because no amount of money overrides the pidgeonhole principle. If the city keeps refusing to expand the market rate housing pool, then rents (and by extension land prices) are going to keep rising. Mandating below market rate units or building public housing is putting a tiny band-aid on a larger discrepancy between supply and demand.

It seems to me (SF resident) that a lot of people have some idealized views of the city, and fear that increased density will mar that image. And thus, the tendency to try and use price controls to fight market demands.