The cost of life is lower. Healthcare is included in taxes.
The cost of life argument makes no sense. By this logic we should be seeing janitors, or translators, or piano teachers in SV being paid much, much more then they are. If there was a coal mine near San Francisco I suppose the miners would be paid 100k/year as well?
Thats why someone wouldn't start a coal mine near SF.
People are only going to be paid up to the point where a company still makes money from them. This has a high ceiling for software devs, a low ceiling for janitors.