Why are old games so hard to preserve?
Because a game is not a single file. It is software plus hardware plus an online service plus a bundle of licences, and any one of those failing makes the whole thing unplayable — which is why video games are among the most fragile media ever created.
The technical obstacles:
Physical decay. Optical discs suffer disc rot; cartridge save batteries die; magnetic media degrade; and console capacitors and drives fail.
Hardware dependence. Many games rely on quirks of specific hardware — timing, custom chips, display behaviour — that emulation must reproduce exactly. CRT-era games frequently look wrong on modern displays because the artwork was designed around how a CRT blended pixels.
Copy protection, including physical dongles and disc-based checks, which actively obstructs preservation.
Online dependence, the largest modern problem. A game requiring authentication, a matchmaking service or server-side content simply stops working when the servers are switched off, and for live-service games there may be nothing meaningful left to preserve at all.
Patches and versions. The disc is not the game; the shipped version, the day-one patch and the final version are different works, and the earlier ones are frequently unobtainable.
The legal obstacles, which are the harder half:
Copyright terms far exceeding the commercial life of the work, so most games spend decades unavailable and protected.
Fragmented rights. Music, engine, middleware, fonts, likenesses and brands may each be separately licensed, frequently for a fixed term — a lapsed music licence alone can make a re-release impossible, and is a common reason beloved games vanish from stores.
Anti-circumvention rules, which can make bypassing protection unlawful even for legitimate preservation.
Rights holders who cannot be identified after studio closures — the orphan works problem.
Who is doing the work: national libraries and archives, dedicated game museums, university collections, and — substantially — volunteer emulation and archival communities, whose legal position is precarious even where the cultural value is not in dispute. Studies have found the overwhelming majority of pre-2010 games are not commercially available in any form.