A lot of it was incorporated or duplicated in feedback control theory, but mostly in the context of industry, so it didn't really feed back (heh, sorry) into other, more academic, areas. And, on the other hand, it spun off into (IMO) fluffy "second-order" cybernetics and became a kind of toy philosophy.

I find it sad too. PID controllers are great but from my POV they're barely the first step.

However, another way to look at it is, you can study and apply "Intro to Cyb" and leapfrog into the future.