Companies just adjust their definition of "qualified" upwards until it looks like there are too few qualified candidates, then call it a shortage.
A recruiter once told me, if you see 30 applicants for a high level tech job on LinkedIn, not to worry about competition, because ~27 of them were likely to be unqualified trying-their-luck applicants, mostly from other countries where the company was not going to hire, and mostly with no relevant skills or experience.
They told me the actual number of qualified candidates was usually just a handful or less.
I doubt this is true in SV, but I don't live in SV.
If this were true for "qualified" candidates, there wouldn't be a labor shortage, right? ;-)