If you are high skill enough to do a PhD in anything meaningful, why enter into an open-ended low-paid work contract with a professor with no definite end-date on when the PhD is granted? An american has even less incentive, as the reward of a work permit is not on the other side.
Only reason should be that you want to be a professor, research can be done in private companies without this license. 95% of a PhD is worth as much as 0%.
> why enter into an open-ended low-paid work contract with a professor with no definite end-date on when the PhD is granted?
This is less of a problem than you might imagine. While no school will guarantee to give you a degree regardless of your performance, it's pretty close. They don't offer the limited funded spots to anyone they don't think can make it.
The real compromises are that people go into their PhD thinking they're going to cure cancer and become a professor at Harvard, and come out of it having made a 5% improvement to a model for predicting the risk of one particular complication following treatment for one particular type of cancer, knowing that becoming a professor at Podunk College would take another decade of work. Or the decide to quit once they discover the reality of it.
The under-paid indefinite purgatory period is called the postdoc.
There are very few of such roles. Of course PhD is often an advantage when it comes to job application and promotion, but outside very specific roles (think about OpenAI looking for a PhD in LLMs, or Intel looking for a PhD in certain engineering fields), it's more often a nice-to-have.
maybe in CS, but if you have a PhD in a STEM field, you're not going to be looking at a wasteland in private industry for jobs that demand a PhD. Good luck getting a job running a big firm's private research lab without a PhD, and tens of thousands of companies demand that PhD. Chemistry PhD? what company doesn't need one of them, if not dozens. Materials science? yeah, you are going to be finding lots of companies that want their product development team run by someone holding a PhD at least. BioTech and Pharma aren't being run by people who just have a bachelor's, and there are over 10,000 private pharmaceutical research labs. Even your Wonder Bread has more than one food science PhD behind the scenes working on it. Any random big agribusiness alone is going to expect you have a PhD in crop science to conduct trials for pesticide development, and they're going to want a chemistry PhD to help develop the formulation, and an entomology PhD to investigate the effect their product has on insect biology, a soil science PhD to study the effect on soil, biochem PhD, biotech PhD, all sorts of engineering PhDs, probably some statistics/math PhDs...
Now, if your PhD is in the humanities, you're not looking at the same situation. It's almost bizarre they call the degree the same name, since a PhD in the humanities takes you on a completely different path. I don't think many companies are demanding a History or English or German literature PhD. Sometimes this can make you a competitive candidate for a job in a completely unrelated field, but those jobs have no need for a PhD, it's just something that makes you stand out when 100 overqualified people are applying for the same job. So will a candidate working in the Peace Corps. Or volunteering hundreds of hours a year. Those getting a history PhD are competing for the...what, 60? 90? jobs in the entire nation that require a history PhD, which is being a professor that gives other people history PhDs. So of course, you will only get such a job if you go to a top 10 school, and the chances of this are basically less than becoming a professional athlete. So the vast disparity between a humanities PhD which has no sustainable aspirational track, vs. a STEM PhD where you become a qualified candidate for both academia/the government which hires many PhDs, and industry, which also has a demand for PhD-trained candidates. Probably 3/4 of STEM PhDs don't work for a school or the government.
In my rather limited experience, private research was way more productive and enjoyable and I was able to do it and get things working without a PhD. In fact, during my short stay a iRobot I was quite surprised to find that none of the PhD's there could help me with what I was doing or provide guidance.
Later I worked with PhDs and PhD candidates in a university setting. What shocked me the most was the narrowness of their knowledge and their lack of consideration for practical matters.
I'd rather let the market judge my work than an academic committee.
Only reason should be that you want to be a professor, research can be done in private companies without this license. 95% of a PhD is worth as much as 0%.