It's good for new games too! With Lutris I can even install Windows games with Proton on Linux, or choose my own Wine setup. I think Heroic Game Launcher does the same.

Best of all, no internet connection is required once a game is downloaded, unless the game specifically demands it. You can save your installers locally and keep them forever, never needing to phone home. If push comes to shove, install a VM of an old OS, and it'll run just the same. Connecting old OSes to the internet is potentially a security risk. And, as we see here, Steam ain't gonna work on old OSes anyway. You're going to need to pirate the games you already bought if you want to play them again in 20 years.