Other than some software, as far as I know you still have the option to "own" (ignoring copyright issues for the moment) most digital content. By "own" I mean "make a one-time purchase and then download the media onto your own device" as opposed to "pay a regular subscription fee and stream the media to your device."

I think the "erosion" you observe is simply the phenomenon that many people genuinely prefer subscription models to one-time purchases, or perhaps they prefer to not manage their own files, syncing, etc. I don't think there's anything bad about that.