Many of the oldest recordings still work, and can be played indefinitely with an optical needle. The time value of money means the possible purchase by a small fraction of buyers 20+ years out isn’t worth much at the time of sale. It’s only moving forward in time that makes anyone care about these sales.
Obviously not in the interest of consumers but I can see why sellers would go this route.
It’s only copying that’s protected not existing physical copies. It’s the same with a book you get the physical book and that’s it. If the copyright expired then you can do all kinds of stuff with the book that you don’t otherwise get to do, barring a few exceptions that apply universally.
You don't usually get the rights to play the music for large audiences or for commercial use - those cost extra.
If you didn't get those rights then you couldn't even play the CD in the privacy of your own home, as that constitutes a performance of the work.
(Of course I kind of think there's something fundamentally strange with the idea of having to get "performance rights" for a recording that you supposedly own, but that doesn't change the law right now.)