This is because way back when some marketing 'cheese' at Apple decided 'X' was, well "Xexy", and so everything got stuck for a very long time.Apples OS names have gotten confusing to me.
The last version of the pre-UNIX-based MacOS was 9, and the first version of 'X'should have been '10', so MacOS Sonoma should have been MacOS 24 or 25 or something . . .
Anyway, having written that I'm off to find versions of Windows 96 and Windows 9 . . .