I have always been very careful with git histories and often rewrite/squash them before final review/merge. Often my rewritten histories have nothing to do with the original history and commits are logically/intuitively separated and individually testable.

That said, very few people seem to be like me. Most people have no concept of what a clear commit history is. I think it's kind of similar to how most people are terrible written communicators. Few people have any clue how to express themselves clearly. The easiest way to deal with people like this is to just have them squash their PRs. This way you can at least enforce some sanity at review and then the final commit should enforce some standards.

I agree on rebasing instead of straight merging, but even that's too complicated for most people.