Personally, I have definitely noticed many people who have convinced themselves they have to stay despite their miserable conditions. Nevermind they have no family in the area, few friends, and despite their very well paying job they can barely afford food & rent. They could surely never be happy elsewhere!
It's like some kind of bubble, where we imagine the whole rest of the country is a backwater hellhole and won't even imagine we could leave.
No city on Earth is full. (Indeed, estimates of human population growth show planetary population stabilizing at less than one tenth our global carrying capacity, so this is not surprising.) It would be extraordinary for the Bay Area to be the first, and so calls for extraordinary evidence.
Housing is a cost of living. Driving the cost of being alive as low as possible should be a high priority. We should use the tools we have to do it.
We don't need to pack everyone in like sardines. As you already noted, there's plenty of space in the world. (You just have to turn your eyes outside the peninsula).
P.S. I do not live nor aspire to live in the peninsula, or anywhere near it
No other city is full because at some point people decide not to live so tightly packed together, and demand dries up.
Current laws raise prices to enforce low density. That's wrong.
If housing and labor markets were entirely elastic, and those are the only two factors your people need to consider, then "go away" could be a reasonable government policy. But people are more than their income and their cost of living.
Consider a recovering opioid addict making minimum wage. Medicaid for health care. They are recovering, not relapsed, because of great support from their parents, brother, and grandparents, all of whom live in (say) Oakland. If we look at the labor market and the housing market, the rational economic decision is to move away. Away from their family, the support network that keeps this person employable (and quite possibly alive). Should the whole family move? Not all jobs are everywhere. Should the brother quit Berkeley? These webs are not easily untangled.
If their support network were a Church, or a local football club, the cost would be same: leave your life behind so the Bay Area can stay suburban.
Expensive housing destroys the small, vital institutions that hold our society together by driving people apart.