I think part of the reason is we put effot into preserving
valuable art, architecture, etc. Creation effort does not equate to value (of course everyone values things differently but there is a level of majority consensus on certain things).
Modern creations have a much lower barrier to entry so more gets made, which is great, but also makes preservation more difficult. There's hundreds of new games on the App store each week (don't recall the exact numbers). Preserving each one, especially the history of development (art assets, source code, design docs and discussions) would take more time than any organization has and also not be very useful to the public.
Yet there are good, worthwhile, interesting, and historically significant games in that haystack somewhere. How do we filter the noise before the stuff worth preserving is lost?