And same corporations are now pushing BSD license at every avenue just to avoid having to do that.

This confuses the economics of open source. It's easier to contribute changes upstream than maintaining a fork. A smart business decision is using permissively licensed software that is maintained by other teams (low maintenance cost) while contributing patches upstream when the need arises (low feature cost).

Bringing a fork in-house and falling behind on maintenance is a very bad idea. The closest I've ever come to that in industry was deploying a patch before the PR was merged.

Proprietary Unixes were literally that at the scale of an entire OS.