VCs are largely already wealthy, and SF is a pleasant city to live in if you're already wealthy. As such, they have little incentive to move, and so founders will continue to flock there to start their companies.
I completely agree that shopping around for cities should be easier, so that city governments like SF are forced to get their head out of their ass and make their city competitive.
However, until SF becomes unpleasant to live in for rich people, not much is going to change.