Don't you think that if the books that Anthropic orders from New Zealand were available (online) anywhere else, they would order them from there rather than from New Zealand? So yes, I would say there's a pretty big chance that those books are really rare, as those are apparently the only copies you can buy online.

The actual reason to get angry about this is copyright law, which would rather have all surviving copies of a (niche, old, rare but still covered by copyright) book in private hands and inaccessible to the public, rather than make it public domain.