That's a hard problem to tackle at a national level without the dreaded Socialism.
If they want to fix the problem they'd need large tracts of very high grade housing rented non-profit, (never sold) on government land. The competition from this would drive prices through the floor.
A 10%-20% price difference is irrelevant and will just disappear in just a few years anyway.
At some point prices will make employing people there impracticable due to wages and commercial rental. In the current system, that is the price point the market will reach no mater how many units are built.
If anything SF has become more centralized and companies keep paying high salaries and other perks playing in to the whole thing.