The bisect might be easier to do, but it's vastly less useful if you're looking for why and not what since the commits are not actually the authors originals and the state of the project you find is not the state the author authored them within.
For us only the original authors squash and tidy up their own commits so they can add as much context as they want.
That's not to say each PR is one commit, if there are multiple distinct parts of a PR that could be cherry picked in a way that they make sense on their own they'd still be separate commits.
