I am an SFBA (Marin) resident with a fairly large financial and personal interest in the health and welfare of the city of San Francisco - so this is something I think a lot about.
I think your point is interesting and should be considered.
Obviously it isn't literally true - clearly there would be a point at which enough housing could be built in San Francisco to hit any arbitrary affordability number.
However, it's worth considering that any politically and physically feasible[1] amount of development might not satisfy the latent demand, nationwide, for a house in San Francisco. It is not inconceivable that there are literally 2 million people in the US that would like to immediately move to SF if housing prices were in line with, say, Minneapolis or Denver.
I also think there might be a corollary to this with regard to homelessness in the state of California. I have read with great interest about the successful "house the homeless" projects that have been implemented in places like Salt Lake City which appear to suggest that you can solve a cities homelessness problem by building enough units to house that population. But what if there are (essentially, not literally) an unlimited number of people willing to be homeless in California ? What if the Salt Lake program really only works because it gets cold and snowy there and, really, there are only so many people willing to be homeless there and you can, in fact, house them all ?
If either of those are the case, I don't know what a good solution looks like.
[1] Including the time dimension ...
* The bay area
* Boulder
* Austin
* Portland
* Seattle
And so on and so forth - and even right here in Bend, Oregon!
I have a suspicion that everyone wanting to live in all those places probably isn't actually true.
I don't know about Bend but all other cities you mentioned are desirable urban hotspots with (relatively) plenty of attractive jobs.
I find it very easy to imagine the supply of people interested in moving to all of them outstrips supply by so much as to practically be indistinguishable from unlimited.
There really are a lot of people around and there are as many in not more decaying/depopulating areas to compensate for the Austins and Berlins of the world.
https://oregoneconomicanalysis.com/2019/01/29/oregons-housin...
Housing in Portland is catching up to demand and rents are leveling off.
Seattle is seeing something similar. The bay area is not, because they fight housing tooth and nail.
On the one hand, I really don't like San Fran and don't want to move there. On the other hand, well, NYC is eight million people.
The real places this effect kicks in are global status cities like New York or London, where it’s a status symbol in every country’s elite class to have a vacation home there. It may actually be impossible to supply both foreign and domestic demand for residential via the market.
"There's so much corruption that no amount of anti-corruption drives will eliminate it"
"There's so much alcoholism that no amount of alcoholism reduction will eliminate alcoholism"