> [...] Nameservers responsible for archive.is (ben.archive.is, anna.archive.is) are returning answers tailored to the IP address of the requestor [...]
That's "how" not "why". Most major services tailor queries based on the source IP, for some reason when archive.is does it to cloudflare queries it's either broken or purposefully broken. At first I thought it might be something to do with 1.1.1.1 in the archive.is network but then I noticed cloudflare queries on behalf of clients don't even source from that IP.
Archive.is intentionally returns bad results to Cloudflare DNS, because Cloudflare don't send them the EDNS Client Subnet Header. Archive.is haven't said much about why, but what they have said appears to accord with this blog post: https://www.sajalkayan.com/post/cloudflare-1dot1dot1dot1.htm...
From this thread https://community.cloudflare.com/t/archive-is-error-1001/182...