This is a stupendously, jaw-droppingly cynical take.
There is no way premium connectivity is making them any significant amount of money. It is so cheap! $100 / year last I checked. So Tesla is not basing any product decisions on that little pittance of money (remember, most of that money goes to the cellular companies that provide the networks, so the profit if any must be truly tiny).
And premium connectivity brings so much more than just music… video, web, traffic data, remote honk, remote light flash, remote viewing of live camera feed from the car's cameras on all sides, remote climate precooling / prewarming, remote control of other car functions, notifications about state changes, remote monitoring of charging status, notifications when charge is done, notifications of alarms… I mean the list is huge. You get all this with premium connectivity and none of it without.
You say the iOS app is great; connectivity with the car is one of the reasons it is great… I say all this just to make the point that just adding CarPlay would not make any meaningful number of people drop premium connectivity. What CarPlay offers is just a tiny little bit of all this.
So I'd look elsewhere for reasons why Tesla won't have CarPlay (and I agree they won't). Probably because they don't want to give up control of their UI to a massively controlling entity that wants to dictate so many aspects of what happens, and who also wants a cut of everything, including most likely things that are simply free with Tesla today.
There's quite a laundry list of other similarly oddly overwrought complaints that could be responded to above, but the only other one that really sticks for me is that sentry mode playback is indeed very flaky… but you know, that will be fixed in a software update.
Long story short, expecting CarPlay when Elon and Apple both want total control is a non-starter. CarPlay has too much baggage in the form of Apple control.