And there are numerous places in Germany and Northern Europe where an experienced developer can command €80-90k.
Consider that a senior position at Amazon Berlin wich lists €80-100K range would be more towards €300k in Bay Area.
That's not what I wrote. I said they pay as well as others in the area. Yes, not everyone pays exactly like Google or Amazon, but other tech jobs in the Bay Area are also far above national median for developers. FAANG pays well but they still pay in relation to the area, they don't just give away $300k paychecks to people anywhere in the world.
And the rest also just confirms what I mean, 80k in Germany are a great salary. Many people won't gain much moving to the Bay Area to get $250k (if they can). The standard of living won't be that much higher than with 80k in Berlin.
For many people staying close to the place they grew up and their family is important. If you get a well-paid job there it can be more attractive than moving halfway around the world for more money.