I'm pretty sure that I've never seen any OS/Linux distribution set default EDITOR to vim. If EDITOR is set to vim, then someone must intentionally did that.

Right. Many programs react to an unset EDITOR variable by assuming vi though. This makes sense, of course, as virtually all systems are going to have some implementation of vi installed. Even the almighty ed tends to be missing from the default install of some recent Linux distributions.

Only if they have wrongly conflated EDITOR and VISUAL.

That's probably out of mercy- saves people from getting stuck in ed.

git bash on windows has vim as the default editor when editing commit messages

Maybe someone should file a bug to them? I don't think vim is a sane default value for EDITOR, but I have no idea whether there's any sane alternative on Windows.

I believe POSIX defines vi as mandatory visual text editor, which makes it present on any compliant OS and thus a sane default value for EDITOR.

Technically it's part of the optional "User Portability Utilities" feature group, and so is ex, the only mandatory editor in POSIX is "ed".

'nano' is fine

I switched to nano recently, and it wasn't as easy as it perhaps should have been: https://stackoverflow.com/questions/36802996/bash-nano-comma...

In OS X it is vim.