It's a matter of supply and demand. If the zoning laws enable the building of affordable housing then the supply would rise and overall prices would decline. What you'll find in places with high housing cost is that zoning laws or geography prevent massive expansion of housing supply.
Right, and there's a reason for that: a decline in housing prices would be seen as a disaster, because so many people have so much of their wealth tied up in home equity. Of course, it doesn't have to be that way: if you happen to own a single family house in SF, and it gets upzoned to allow apartment buildings, you can expand your house and become a landlord, or just sell the house to a developer to replace with an apartment building. But both of those options are harder than just sitting on your land and watching its price grow, which is part of the "American dream" of housing as a store of wealth that people were sold.