How to restore unavailable songs in my Apple Music Library?

Is there any reason to be finding that more and more of my music library (Songs I've purchased from iTunes back in the day, CDs I've bought and burned copies into my library etc) are becoming 'Unavailable'?

I thought they legitimately belonged to me and should be kept in my music on my account, so I don't understand how they are unavailable. I'm annoyed as I've since got rid of the CDs (Because who has a CD player anymore??) and now I can't listen to the albums.

I've had the same Apple account for over 15 years & I've maintained my library through all the changes from iTunes to Apple Music.

Super frustrating and quite a scam tbh.

Anyone with any insight please let me know.

[Re-Titled by Moderator]