Documentation like that is written by specialist technical writers in cooperation with engineering.

Corporations found out that they can skimp on that and still get paid.

Yep. I haven't seen a technical writer position since the early 2000's, at an enterprise SaaS company (we called them "ASPs" back then.)

It was the golden age of computing. Today’s best in class documentation (Stripe!?) doesn’t come close to average documentation in those days.

They still know. They're just not told/incentivized to do so.