It still quite hard to achieve FI early, even on a tech salary.

I can't speak for San Fran, but I'm on a pretty good (by UK standards) tech salary in London. The cost of living (rents mostly) still make putting a high % of salary away every month a challenge. If you have kids as well, it's almost a non-starter.

The marginal tax rate means the only mechanism to do this efficiently are via pension contributions (similar to a US 401k), and these are locked until age 55 (60 by the time i get there).

Financial independence in your 30s is an enormous privilege.