If I had to guess, aside from "inertia" (which I suspect is the major part of it), another answer would be that iTunes is pretty much their one Swiss Army Knife app on Windows, and if they split iTunes out into multiple parts on the Mac, then they'd need to do the same on Windows. It's not a good reason, but it's my guess. I too would like to see a Music.app on the Mac, that focused on music, and a Videos.app for movies and such (ugh, I still don't love TV.app), and maybe a Media Store app for buying music and video. Rather than having iTunes be the "jack of all trades".How about apple make a special version of iTunes which only contains music?
Ah, but one could reasonably argue that none of those business partners should be upgrading to Mojave yet. Wait for a .1 or .2 release, and extensive gamma testing.Mojave doesn't obviate the needs of those business partners.