[tlamponi]

The core reason for this is that lots (all?) of "modern" mail user agents (MUA) mess with whitespace in their default configuration, which breaks patches as the indentation is all of and git is confused.

git send-email is made for this, and handles all edge cases correctly, but depending on your MUA and/or it's config, it can work pasting patch diffs in there just fine – the point is that, especially for newcomers, and for a few edge cases, it may hard to do correctly and so using the tool made for the job avoids friction for all sites.

ps. ZIP wouldn't be required, just use base64 encoding, that's basically what git send-email does, depending on the encoding, line length, ... of a commit.