But they contain a large equity portion. And over 2-3 years that equity portion ends up being more than the base salary, and you can get pretty close to a Bay Area compensation range.
e.g. I was L4 @ Google Waterloo in Canada. Base compensation was nothing special. Good for the immediate area, but not stellar. Yes, nice perks, amazing benefits, decent vacation, good bonus, etc. But after accruing RSUs for a few years you're probably making double what you started with. Especially so if the stock goes up a bunch.
Could you make more money working directly for Google in SV? Certainly, but your cost of living would be way higher. But even if you stay home you're likely making at least twice what your peers in the regular local companies are making.
Unfortunately it's terrible golden handcuffs, because nobody else in the region will be able to match that compensation package.