Academia just isn't WORTH it for talented peasants (speaking as one).
I had people encouraging me to go into academia since I was 4-5 years old, had a desire to go be a professor, etc. But things have changed a lot since I was a child 30 years ago. Now, if I were to go into academia without family or other connections, I'm looking at:
- Unstable employment and a serious amount of overwork. At the end of this I may get a chance at some stability, but given how academia is moving away from the tenure-track, that's less and less likely.
- Restrictions on what I can say and what kind of work I can do based on academic politics, what grants will fund, etc.
- Very little reputational benefit to affiliating myself with an institution: speaking as an American, our institutions are collapsing. Why would I tie myself to a sinking ship? Those who are already in the upper-middle or upper class are all in on maintaining the status quo because it works for them and because they have a safety net if things go south. It's similar to how, no matter what your interpretation of Jan. 6, 2021, I bet there's some reconsidering of people's desires to be staff in Congress. ("I'm not getting shot for Pelosi/McConnell, fuck that noise.")
On the other hand, if I DON'T go into academia, I can still access research and I can say whatever I want. I can also work on my own schedule and only do work that I think has some value (as opposed to chasing after publications and massaging my work to beef up my CV).
Anyone from a poorer background who has the skills to make it in academia also has the skills to recognize that it is a TERRIBLE deal for them at the moment and that they have better options.
Granted, this is also true of higher socio-economic classes, and that's one reason the people from elite backgrounds in academia are also trending towards the more and more mediocre.