That, I agree with. San Francisco should have built more housing to accommodate the growth. Though if people are leaving already, I can also see why developers might have been reluctant to bet too big on new construction.
Because if "tech elites" actually are leaving, then the increase in demand will have been proven to be transient
Surely many developers would have made the bet anyway, at least in 2010-2019, but going forward it'll be worth considering whether building housing for people who are likely to leave en masse is worth the risk.