$ sudo chmod -x /Applications/Music.app
This was a common complaint I have heard from those coming from Windows/Android and even Linux... It's unix.
Also, the play/pause key works with other apps. Other default apps can be set.
Many other valid points in this article and thread, but I don't know why people expect the default behavior of the play button to behave any differently when no media is playing. Music.app may have an upsell, but it's still a place to organize your own personal music library. No cloud or SaaS required.