You hold a small to mid conference in SF and the plurality of your audience and presenters will not need to pay for a place to stay. That means the quality of your conference will increase significantly.

Place it in another major city and they can easily fly there and find a place to stay there. Being a major city their companies may have subsidiaries there so they may be able to do other company work and add this onto a company trip.

And if you’re an international conference, you should probably limit yourself to something like 5 cities or else everyone from outside the US will likely struggle and not be able to make a real trip outside of it.

Holding conferences anywhere outside major cities does not seem to make any sense to me.