Many politicians and tech ceos have discussed a severe shortage of US citizens getting advanced degrees in STEM fields. Here's one such link. There has also been legislation proposed that would have made this a formal part of the immigration system, again specifically for advanced (preferably PhD) degrees in STEM fields (notably not law, medicine or business). The legislation did not pass, though largely because it was bogged down in part of a larger (and failed) effort to negotiate a general immigration system.

https://www.computerworld.com/article/3089314/it-careers/cli...

This isn't the entire issue, I'd agree with that. But it is definitely a relevant piece. And it is notable that tech ceos and politicians are calling this a "shortage" when organizations like RAND are simply seeing a rational, market-based aversion to certain fields.

I'm in the odd position of completely agreeing that the US should have a skills based immigration system like many other countries, but opposing a particular focus on STEM, as I don't like the idea of coercing would-be immigrants into studying this particular field as a condition of coming to the US, and I don't agree that there is any "shortage" that can't be explained as the product of rational decision making about careers.