They won't because they don't have anywhere near the same access to capital. There is no country even close to the US in this regard, and US salaries in software engineering are the exception, not the norm.
For example in India it used to be only outsourcing, but now they are launching their own startups as well, some quite succesful. Slowly the capital will start accumulating there as well. And that is a good thing, for global inequality.