We've been producing far more PhD graduates than we need for decades. Each year a relative few get jobs (e.g., university professor) appropriate to the training, while the rest are unceremoniously dumped by the railroad track to fend for themselves. Same for MS, BS, BA et al. Overall we have far more highly-trained people than we need for most all degree programs.
It's not like the USA needs a butt-load of "math PhD's".
Having an excess PhD level citizens is every free countries wet dream. Its bonkers that people think it is somehow a negative.
It is a recipe for innovation. Most of those people want to do things with their knowledge, not teach classes. Most go to business who use that knowledge to innovate and increase profit.
Businesses literally get an excess of highly educated workers for (almost) free, and for some reason the MBA/Tech-right class thinks its a good thing to blow up that system. Absolutely bonkers.
We've always had an excess of PhD's. They're made to purpose for university instruction or research. But there are far more PhDs than appropriate jobs:
The purpose of a PhD is not to train people for "appropriate jobs". PhD students perform a large part of academic research, and while most of it is grunt work and produces incremental results, some brilliant people end up discovering a gold nugget and carrying their field forward many times over.
Innovation is hard, most ideas do not pan out, and most people aren't made for it. It really is a number's game: to stay competitive and innovative as a country you need enough people pushing against the frontier, including taking bets that are too risky for the private sector.
The situation certainly sucks for the actual PhD holders. Go through 5-8 years of intense work and minimal pay, and the outcome is maybe a 10% chance of getting the job you want?
It's unsustainable. I got my PhD 20 years ago, but I would certainly advise my children to avoid it.
You're assuming all PhD's want to become a professor tho. Plenty of people go to graduate school as a mechanism to increase their prospects outside of academia. Or even if they do want to become a professor, they hedge with other roles that require/benefit from the degree.
It's not like the USA needs a butt-load of "math PhD's".