Discs do matter in one way. I don't think I have ever seen a digital "purchase" of any significance which I could resell or gift at a later time. Some "in game" things are resellable, but only within the game's ecosystem. All digital games, music, movies, ebooks, audio books, etc are not (AFAIK).
So if I get tired of my DVD movie collection, I could sell it or give it to my kids. If I ever decide I'm too old for the retro game cartridges I have, they could go to future grandkids. But my GOG games or Bandcamp music is stuck with me forever (legally speaking). Nobody would know if I "gave" them to my kids, but there certainly is no way to resell them.
Now this is still a rights issue, but physical media makes this easy (outside of keys/DRM as you point out) You always have the right to hand on a physical object.
So if I get tired of my DVD movie collection, I could sell it or give it to my kids. If I ever decide I'm too old for the retro game cartridges I have, they could go to future grandkids. But my GOG games or Bandcamp music is stuck with me forever (legally speaking). Nobody would know if I "gave" them to my kids, but there certainly is no way to resell them.
Now this is still a rights issue, but physical media makes this easy (outside of keys/DRM as you point out) You always have the right to hand on a physical object.