Why do games disappear from digital stores?
Usually because a licence expired — and the result is that a game can become genuinely unavailable to buy legally anywhere, which is the core of the games preservation problem.
Why games get delisted:
Music licences. The most common cause. Licensed soundtracks are typically agreed for a fixed term, and when that term expires the game cannot legally continue to be sold containing them. Sports, racing and skateboarding games are repeatedly affected.
Brand and likeness licences — real cars, teams, players, films, comics. A game built on a licence becomes unsellable when it ends.
Publisher or studio closure, or a rights dispute leaving no one clearly able to sell it.
Server dependency. Online-only games become unplayable when servers close, and are delisted because selling something that does not function is untenable.
Replacement by a sequel or remaster, sometimes deliberately, to avoid competing with the new release.
Platform transitions, where an older storefront is closed entirely.
Why this is a preservation problem. Unlike physical media, a delisted digital game cannot be bought second-hand. There is no legitimate market at all. If you did not buy it before delisting, there is typically no lawful way to obtain it — and the studies that have been done suggest a large majority of games released before a certain point are not commercially available in any form.
What happens to games you already bought. Normally they remain in your library and re-downloadable, since the licence to sell ended rather than your licence to use. But this depends entirely on the storefront continuing to exist and honour it, and it has not always held — which exposes how much "ownership" of digital purchases actually rests on a company's continued goodwill.
Why archiving is legally difficult. Preservation organisations and libraries hold collections, but copyright exceptions are narrow and in many jurisdictions do not permit remote access, so a preserved game frequently cannot be played by researchers without visiting in person.
Emulation and community archives fill the gap in practice while occupying contested legal territory.
Campaigns have pressed for publishers to leave games playable after server shutdown.