Many countries require a copy of each book published there to be submitted to their national archives/library. The US has had this requirement since 1790 as far as I can tell.

All countries I checked (Germany, France, Canada) seem to have similar requirements. WIPO claims that this is the case in the majority of countries (https://www.wipo.int/documents/d/copyright/docs-en-registrat...).

Thus, most books should not be at risk of getting permanently lost due to these practices.

This is Anna's Archive (ab)using a current controversy (which I think is based around emotional appeals and distorted facts to create outrage over a non-issue) to tongue-in-cheek advertise their open pirate library.