Isn't it a solved problem? US universities attract best students from all over the world, from practically every society/country/culture. It's way more diverse, selective, and productive to let universities to decide who gets to come than a rule-based system via DHS.

You will have lots of departments or entire universities dedicated to giving foreigners degrees for cash.

I am sorry if I come across any condescending, but that is how most of the current masters programs are operated. Generally, masters are considered cash cow programs that funds other research and also brings a lot of commerce to the college towns. There are some exceptions, but most of them do qualify for my hypotheses.

That being said, why is it a bad thing then? If the people are spending money to get some quality education that can be regulated within United States, then I don't see any downside in delegating the vetting process to the universities. 4 years in the United States, one family visit per year and it brings a lot of commerce to the country. If they don't perform well, then it's always upto the university to make the judgement.

Because then universities are materially interested to let everyone in. With job offers the company is both spending extra, and needs the candidate to actually perform well in the position.