There's a large amount of people in other cities willing to move to San Francisco if the wage is higher than their current wage + moving and cost of living differences. That drives wages up in those cities by either paying more to keep employees or now needing to compete for a smaller pool of employees. The same pull on employees pulls people out of other industries into tech as well which should drive up wages.

The wages elsewhere aren't going to go up as high but it should have some upward drag