Games in general are a very difficult thing to preserve because of how they are often "on-going" things rather than definitive objects like books or films. Minecraft has gone through 27 major version updates, most of which having had in the range of 3-10 sub-versions. So that's potentially ~100 versions, just for Java edition. Should all of those be archived? Or just the final version, when it one day arrives? At this point, the Minecraft from 2014 and from 2026 are completely different games. And at least for Minecraft, there's mostly just stuff added. What about games in which major features regularly get removed, like Fortnite? There, the "last" version will lack many of the games most famous attributes.
Maybe we should just accept that big online games are more like cultural happenings than media objects. In the future, you simply might not be able to play Fortnite, in the same way you can never visit Woodstock again. It's just something you had to be at.