I know you know this, but I just wanted to clarify that international PhDs are not leaving because of a lack of encouragement, but that their F1 visas (which I also hold) stipulate that they must prove they have every intention of returning back to the home country.
Obviously, the F1 forces students to leave once they graduate.
The system is set up to actively discourage students to stay. I don't know which organization came up with the idea of using public money (because most will be funded this way) to educate people and then make them leave. It's somewhat bizarre, and doesn't seem to benefit the US at all.
The obvious answer is that supply and demand applies to all things. If there wasn't this bountiful supply of cheap labour, then the budget would have to cover paying the market rate to American lab assistants. The US has decided to trade a short term advantage - cheap lab workers - for a long term disadvantage - educating its competitors.
Obviously, the F1 forces students to leave once they graduate.
The system is set up to actively discourage students to stay. I don't know which organization came up with the idea of using public money (because most will be funded this way) to educate people and then make them leave. It's somewhat bizarre, and doesn't seem to benefit the US at all.