rebase vs rebase -i

Why does git rebase use format-patch + am, while rebase -i uses cherry-pick?

Just curious. In particular though, it seems especially odd in this case:

$ git rebase --onto <newbase> <upstream>

vs

$ env GIT_EDITOR=true git rebase -i --onto <newbase> <upstream>

Both in theory produce an identical end-result, while using two
different implementations.

(Here I'm setting GIT_EDITOR=true just to demonstrate that I didn't
change the list of commits in the latter case.)

j.