Linux, MacOS and Windows have been completely rewritten multiple times across their existence.
So it's not like the original decisions are all still in play.
Windows and Mac OS were rewritten under some particular weird duresses of closed source profit driven engineering; so it has been a mix of improvements and seemingly illogical setbacks.
Linux developers still need to eat, so some of the same (corporate) influences are there.
But the average engineer who sets out to create a brand new completely modern operating system - usually decides to reuse any components of Linux that they don't have any concerns with...
Which usually gives us yet another cool new Linux variant.
But sometimes we get...
something very different
A cool new FreeBSD variant!
As long as our health is perfect, of course.