I am not following your logic, based on your numbers . Given the huge installation base of 1.3 billion , 40 million Apple Music subscribers is insignificant, and in no way does it show Apple users are loyal to Apple when it comes to services.
You may find that, given Apple is partnering with amazon for thier insignificant 100 million , suggest that 1.3 billion means very little. Why partner with such a small player if you have 1.3 billion user....... Apple Music can help you answer that question, even with such a huge installation base and AM notification and free trials, Spotify is still ahead . You would be shocked how many of those 1.3 billion use Spotify actuallly .
Please feel free to provide facts to support Apple users are loyal to Apple services cause they own an Apple product .