[I keep wondering why Apple changed the OS name now. I would understand if there was a major overhaul but it doesn't seem the case here. Maybe an interface re-design or whatever.
First, Previously to this release did their major competitor have "10" in their product name? ( Mac OS X (ten) is competing with Windows 10 ( skipped 9.... right to 10. ). ). Being dissimilar to Windows is part of Apple/Mac marketing identity.
Second, Apple introduced in the last year WatchOS and tvOS. Hmmm, cue Seasme Street music
" one of these things does not look like the other,
one of these things just isn't the same,
can you guess which one before I finish my song. "
iOS , watchOS , tvOS , Mac OS X
as opposed to
iOS , watchOS , tvOS , macOS
before there was watchOS and tvOS which one was "different".
The naming convention is being merged. That doesn 't mean the content is being merged. watchOS and tvOS are basically
forks off of iOS. That is the opposite of merging.