The reason it's expensive is or because the US is bigger. It's because the people in cities want to keep people out so they make it very expensive. Which in turn fuels homelessness.
The desire to exclude, the refusal to permit enough housing, and the rejection of density are the fundamental cause.
The scale of the US has nothing to do with it. It's merely a cultural choice by a prior generation that younger generations have not yet been able to overrule. But they will.
The answer is to just build a lot more housing. Increasing the housing stock by 10% everywhere would be a good start. If there is so much housing available that buyers don’t get into bidding wars and landlords have to struggle to find tenants, then prices will come down.
Why doesn’t this happen? Because developers will have to do more work for less money.
More housing is absolutely the answer. But your cause is wrong.
The impediment to housing in California is capture of land use policy by homeowners and landlords. We should expand the category of home builders beyond developers, but developers make zero money when they are not building. So developers are not holding back housing in California. The few remaining developers in California tend to be more land bankers than developers. But if we made the process for decelopnrt straightforward, then small builders and contractors could build all sorts of projects. At the moment the process is so complex and difficult that getting approval to build on a site is a hugely valuable financial product that increases the value of a parcel of land significantly (though necessarily less than the cost of getting that approval).
The reason we do not have enough housing all comes down to that NIMBY neighbor who doesn't want to allow apartments anywhere nearby and who has also been given lots of wrenches to throw into the process of approval. We don't have that sort of approval process for single family homes, it's a night and day difference. Anybody is allowed to build a massive mansion without any community input, but for anything more affordable, neighbors can veto it, and do.
The desire to exclude, the refusal to permit enough housing, and the rejection of density are the fundamental cause.
The scale of the US has nothing to do with it. It's merely a cultural choice by a prior generation that younger generations have not yet been able to overrule. But they will.