These institutions receive an abundance of high-quality applications every year and choose only a few; for every admitted international student, several amazing domestic applicants are rejected. The government does not need to bend over backwards for the international students who won the admissions lottery, because they already have a huge advantage. Rather, it might prefer to fight for the interests of its own citizens, whose advancement is in their personal best interest as well as that of the nation.
If an international student follows the established legal processes whereby a foreign person can become an American citizen, he, too, can benefit from a system that protects the interest of American citizens.
This can be especially easy now as the universities target to become 100% online and the number of students whom you can let attend a lecture is virtually unlimited.
They aren't taking away seats from domestic students. They are subsidizing the ability for more domestic students to study there.