ucbalumnus wrrote: “Yes, if the numbers game of producing far more PhD graduates than replacement level exists in other fields where the non-academic research job demand is low, graduates in those fields (biology? humanities?) may face an extremely competitive job market for the kinds of jobs that they have been preparing for.”
It is happening now in humanities and social sciences. Another factor is the shift of many academic employers to producing student credit hours (SCH’s) using distance/remote instruction and adjuncts rather than tenure-stream faculty. In my social science field, which I entered a few decades ago, college enrollments were still expanding, remote/online instruction was non-existent, and so the academic career stream was quite open to talent. While in the social sciences there are also many non-academic opportunities for PhD’s (in government, industry, etc.), teaching-research at a PhD-granting institution may well be the most difficult or crowded path.
That being said, as has been mentioned, PhD’s in technical and science fields do have alternative career routes. This has been true for a long time. One of my brothers is a physics PhD (Caltech) who never sought an academic career but had an excellent one at a national lab; published in the major journals; retired with a pension and continues to consult in private economy.