Firstly is the proliferation of games and their quality. Anyone can make a new game, given an engine and a few art assets. It doesn't take a lot of capital or know-how to release a new game. Therefore, there's a glut of games on the market, from high to low quality, and there are far more than any rational human could ever purchase or play. This was a problem from Day One: When I purchased my Atari 2600 console (or rather my parents purchased for me) my sister and I quickly filled up a 50-cartridge shelf with games where we barely even played or scratched the surface. They were disposable! When we got a Commodore 64, there were more 3rd parties on the market, making games we never heard of, and these games were so deep and thick that one of them could've kept us occupied for 6 months, but still we chewed through them as fast as we could afford.
Secondly, aren't most all the games now oriented around MMOG "communities" and multi-player-based? That makes preservation practically impossible. If you've not only got to keep the game servers running, but you've also got to preserve the community that goes with them... well, forget it. Gamers grow up, their tastes change; they move on.
I enjoyed a few games, years ago, that basically turned into ghost-town servers. Many of us were so tenacious and dedicated to that specific game as it was, yet the new influx of players dried up, and nobody could prevent that from happening. Every newbie was a ban-evader. Every rich opponent was paying real $$$ just to stay competitive. Our precious game jumped the shark and we couldn't let it die. But die they must. I propose that most games are not worth preserving. Perhaps games should be enjoyed where they are, and then left to die, because they will never be the same again.