To each their own. For me, I really like the Discover Weekly/Daily features to discover new music and I can’t see how I would ever “already have MP3s of all the good music” since that’s an ever changing set. Heck, I still have a ton of old mp3s I used to rip and/or download, but I haven’t listened to them in a while.
I would gladly pay for a similar AYCE movie subscription, but I refuse to sign up for a ton of different services and play the “which service is that movie on again?” game. Instead it’s a very different approach for me.