Unix stuff has only recently been "in the norm" for dev related workflows, it used to be entirely Windows only.
Same with office workflows, games (both playing and developing), graphics, etc.
Unix is the rebel here. It is bringing the diversity.
(Currently my workplace is probably 80% Mac, 19% Linux, 1% Windows, but I can see their point that it would be a lot easier to administrate if they were a monoculture of Mac).
The world is bigger than the desktop.
Already your assessment regarding AIX being dead, when it is one of survivors from UNIX/Linux wars shows how your Microsoft hate blinds your judgement.
If the framers of the Internet had not been faced with disparate systems all speaking different languages and protocols, if they had not been introduced to computing as a babel of vendors all wanting to do their own thing, then perhaps they would not have longed for vendor-neutral, interoperable protocols, such as we have today.
The drive in the 70s to hook up very different computing platforms and have them all talking to one another, that's what gave us the Internet today. Perhaps the choices in OS have diminished since the demise of proprietary systems and bespoke OS for so many platforms, but from where I sit, I still see a wide diversity of devices all connecting to the same Internet, all speaking the same protocol, and I'm thankful for that development.