Why can't I migrate Apple Account purchases due to Apple Music and iTunes music?

I am unable to migrate purchases. Settings refuses to explain why; so I am left with calling Apple Support. They tell me the reason is because I'm a developer- oh, wait, no, it's because you were an Apple Music subscriber and/or have iTunes music (like back from the time period when you could put iTunes music on an iPod.) I do actually have Apple Music and iTunes music. So now I can't migrate purchases because of something I did without thinking there'd be consequences. I am sad. Fix this. Tell us why we can't migrate and how to fix it in settings.

[Re-Titled by Moderator]