Traditionally "Mac OS" -> "[Mac] OS X" -> "macOS"

It was often compacted to MacOS for various reasons, like brevity, keyword searchability and tagging.

I dunno, it's hard to get better search ability than what we had with "osx". Among other things, there are a lot of code bases with Mac OS 9 code hanging around in directories named "macos".

Apple has now standardized the names: iPS, tvOS, watchOS, macOS.

OK, but this page is made by Apple.

When you have a name for over a decade, you tend to have it hard coded in a bunch of places...

On the other hand, the official name was 'Mac OS X' until 2012.

Sure, but it was nearly always just referred to as "OS X", so the official renaming in 2012 was just moving it in line with how people already referred to it.

Yeah, my company moved offices a few months back and we had the old location in a surprising number of places around the codebase.

Not really. "iOS" is standard and no resistance has been noted.

So if one thing is true then other similar things must be true!!!

No resistance is overstepping, as far as I remember a few had a hard time foregoing iPhone OS initially. But that's maybe not what you're talking about.

Lowercased i titles are / were / have been common and comfortable though. Some of them even before iOS.