They are taking money from their home country and spending it in the US. It is like anti-foreign aid.
From the perspective of the students, yes, there is a financial transfer to the U.S. However, from national perspective, there is an economic transfer to the other nation. The U.S. university system represents the product of decades (centuries in some cases) of public and private investment. Foreign students and the societies they return to get the benefit of that investment - a better educated than could be trained locally - without having made it themselves. Hence, an economic transfer from the US to the other nation.
Having these type of students go back is not a lose. In fact they bring with them a demand for American goods, and culture.
I think it would probably be better for everyone if we streamlined the process of transitioning from an H1B to permanent residency, and it would definitely be better for the US economy.
There is some exploitation that happens, but by and large people are going to pay market rate +-15%, minus administrative costs. Administrative costs for hiring immigrants are extremely high, so it makes sense that their wages might be a bit less. (The best way to raise their wages is to reduce the administrative costs.)
The system as it is structured right now is basically designed as a foreign aid program. It encourages foreigners to come to the US, get a degree, work for a few years while saving a lot of money, then go home and invest it in building a new business not in this country.