Average income is heavily skewed by unskilled workers who constitute the overwhelming majority of the workforce, as well as workers with less than a high school degree which constitute the overwhelming majority of the workforce.
I actually agree with you that 90K gets you top-10% of the developers in many countries, but you were saying that 45K would get you a great developer with 10 YoE.
Devs with 10 YoE are already probably less than 20% of developers, and there are devs with 10 YoE who aren't "great" developers. Perhaps this is my own western near-sightedness talking, but I'm under the impression that great developers may constitute fewer than 5% of developers in some of these countries in question (I assume due to a combination lower English proficiency which is important for working with Western employers, different cultural norms which cause many developers from some countries to adopt anti-patterns for working effectively with teams, and more limited access to reliable internet and better equipment, which could result in lengthened feedback loops during their learning process).
But my primary argument wasn't that you'd be unable to get a great dev with 10YoE, it was that you'd be unable to get two great devs with 10 YoE for 90K/yr, or 45K each, or as tpacek pointed out, more like 35K/yr take-home.
