I've always wondered if there's a story behind modern.ie using chunked .rars over e.g. non-chunked .zip.

What were the technical/human constraints that lead to that solution? Was the team agonising over conflicting goals? Or was it as simple as "Alice already knew it"/"Our tool chain already supported it"?

That's often but not always true: if you use VMWare on Linux or use an OS which is configured not to run arbitrary executables you can't use the self-extracting file. I certainly wouldn't say those are common problems or insurmountable but they're in the class of things which you simply don't need to worry about with ZIP.

What's wrong with .tar.gz like most other *nix software uses for downloads?