> We would also often find 10+ email addresses associated with a single one-line change commit, which I found quite odd.

To be charitable: could have been that the commit started off big and complex, getting modified and reviewed by several people over time... before one person finally figured out how to simplify it down to one line — and so then they rebase-squashed it down to just that line, rather than polluting your commit history with all the intervening nonsense.