I wonder if there are cultural differences that mean the Japanese don't have a strong sense of nostalgia and thus are not as interested in preserving history in general.
I've thought about this as well. This mindset of preserving digital media seems to have been largely driven by Western organizations/individuals. An example of this cultural difference is the number of takedown requests by artists against Western sites like Danbooru that repost their art from Pixiv. There was also a notable case of a game developer requesting that all her future games not be translated into English after seeing people repost her art without her permission.
Segawa has requested that English translations of her games (TOWER of HANOI and onward) no longer be made. Though she understands it's ultimately a small minority, the frequent reposting of her art and the like by English users upsets her whenever she sees it, impeding her ability to create and forcing the difficult decision to forbid translations.[0]
The overall feeling I get is that the community generally considers the author's will to be of highest priority, even if following it is detrimental to the long-term public cultural heritage.
Creators can and will occasionally use it as a weapon - when someone uses their art in a way they deem offensive, they may retaliate by pulling their art from the primary distribution site, and requesting anyone who has them to not re-upload them. The community will generally comply, and will berate the offensive-art-user (not the author) en masse for causing the loss to happen. The general distrust against danbooru et al I think stems from the lack of conformance to this "word of god overrules everything" mindset.
Not sure if it's related to the above, but Japanese copyright law protects moral rights (chosakusha jinkaku ken 著作者人格権) much stronger than the US does: they apply to all works, and cannot be transferred nor waived. The most you can do is sign a contract agreeing not to exercise them. There have been lawsuits in the past where selling a PlayStation memory card with a hacked save data of a game was ruled as a breach of the work's integrity. https://ja.wikipedia.org/wiki/%E3%81%A8%E3%81%8D%E3%82%81%E3...
Reposting other people's work is extremely looked down upon in Japan. Danbooru-like sites won't survive a day if hosted in Japan. (People do secretly use them though.)
I have a suspicion that what we did to them in 1945 could certainly have had an effect on causing them to become not too interested in preserving history.
While that might have some effect, my understanding is that it predates that by hundreds of years. For example, they regularly tear down and rebuild some structures of historical significance.[1]
I suspect it's to do with copyright law. Copyright is extremely strong in Japan and there is a cultural pressure not to do the "wrong thing". Preserving old games etc is legally ambitious and this is often ignored in the west. EDIT: person below me posted the same opinion!
