They're doing it to each other.

Cloudflare is pretty much the only DNS resolver that doesn't provide the source user's IP address when doing recursive requests.

Archive.is is pretty much the only (big) website that refuses to answer DNS requests at all if they don't include the source IP address.

Cloudflare argues that this improves privacy (nevermind that the user's IP shows up anyway as soon as they try to actually connect). Archive.is argues that this prevents them from doing geographic load balancing (which, as it turns out, just happens to be a separate product that Cloudflare is happy to sell to websites).