Most people who squash things have never used git bisect, cannot solve a merge conflict and when there is one will just delete the directory and clone everything again. I've worked with such people. They can go on like this for an entire lifetime.
For me (I know you used most, not all). A PR is an atomic thing. Either one bug or one feature. Commits inside it are mostly time snapshots, and fixing formatting and linting errors. If I where to properly present the PR, it will also have been a single commit.
I used git bisect once in 10 years, and it was when I learned about its existence.
I am convinced that very few know about git bisect, much less use it regularly.