I get your point and have considered it myself. It is a big problem, but it is also a function of the rather rapaciousness of the US economic/immigration system and model itself. NOTHING would stop the US government to fund the opportunities in whatever country in question, but also, there is no reason why "immigration" could not be a kind of skill building/sharing and development plan where you are given the opportunity to go to the USA for a set number of years and/or cycles, and then you know you are going to transition back to your home country where you will then use those skills/knowledge to help and build your country.
It is actually extremely inefficient the way the rapacious American system in particular works (but also Canada and increasingly the overall EU). There is far more utility to be gained from making exponential strides and advances by the "human resources" as they are even referred to, by uplifting and developing their home country than to serve the US ruling class in ever more desperate search for "growth".
And then of course there is also the fact that immigration is short sighted and a pure measure of the incompetence and failure of government. If you are importing people, you have failed to adequately govern to meet your needs and it also will make you reliant on that immigration while you will ignore even building up any kind of domestic capacity.
Then there is of course the consequence of immigration dependence coupled with international development and growth too when the source of "immigrants" dries up because people will want to life in their home countries where they can be among their own and development has narrowed the difference between comfort levels in the USA. We will be seeing this effect increasingly in the near future as, e.g., Indians see no reason anymore to move to the USA because the US university is not even as good as a local university, let alone American society is crumbling and cracking at all seams. It will be compounding effect. I already see it happening.