As a developer, I've found that it's just not worth it to respond to tech companies / recruiters seeking engineers, unless they're based in the USA. Companies based anywhere else, in my experience, expect to pay
less than half the rate that US companies will pay.
Why is this? There are possible causes having to do with tax rates and culture, but has anyone really looked into it? How big a contributor is this (rather than, say, immigrants as percent of total population, or university quality) to the fact that the US has Google and Apple and Facebook and Twitter, and the rest of the world has… JustEat and Spotify?
https://data.oecd.org/germany.htm https://data.oecd.org/united-states.htm
If you scroll down to the Economic indicators, you will see that on average people in the US work around 1.700 hours a year, whereas people in Germany (and many other European countries) work only 1.400 hours. This alone can already explain 20 % of the wage gap between the two countries, and in fact if you look at the average salary per hour worked, it is almost identical (32 USD), which would support this theory. In addition, many things like education, housing, social security and health insurance are much cheaper in Europe, which leads to lower salaries (as they tend to follow the cost of living). Furthermore, regulations in Europe are stronger than in the US, which makes it more difficult (or sometimes even impossible) to fire people once they have been employed for some time. Hence the risk of losing your job is smaller, which should lead to a lower salary as well as companies face a higher risk when hiring someone, and employees have less risk.
And in extreme tech hot spots like SV or NY there should course be an additional effect due to the high demand of skilled IT professionals and the fact that people can usually find a new job very easily, which also makes it easier to negotiate a higher salary and forces companies to pay above average rates to attract talent, which is a self-reinforcing effect.