Proven that you are worth that salary in a given city. As tech companies realize they are no longer tied to SV they will also no longer have to pay the same high salaries to attract the large but overall still limited talent pool in this geographic area.
For every SF developer there is probably a just as good developer in Boise or Belarus willing to do the job for much less. Why should a SF developer who moves there make more?
People are worth a lot, but they become worth less monetarily as the talent pool grows in size.
Because by doing this you have misrepresented the truth in order to extract more money from your employer than you agreed (presumably, in your employment contract).
(As I commented elsewhere, whether you think paying by local cost of living is the right policy is valid to debate but isn't the point here.)
Did you prove you’re worth the salary or do they just have massively inflated salaries for everyone in a certain west coast US city because A bunch of huge technology companies failed to realise computers and the internet exist outside of said city and remote working is a very workable thing.
I’m not saying they should drop your salary if you move, but I also don’t think a lot of people hired at typical SV rates are actually worth that much, so much as they can’t afford to live there if paid less.