> Most of them ended up with postdocs at equally or more prestigious institutions than the one we graduated from.

Postdocs are not a tenured position. They are just another step in the temp job/contract work level of the food chain.

To put it differently, no one retires from a postdoc.

In my days in academic research, postdocs were humorously described as paid positions to send out CVs and file job applications. The faculty also gave postdocs their own office so that they wouldn't bother undergrads with their crying.