Right, but squashed commits don’t scale for large PRs. You could argue that large PRs should be avoided, but sometimes they make sense. And in the case where you do have a large PR, a commit by commit review makes a lot of sense to keep your history clean.
Large features that are relatively isolated from the rest of the codebase make perfect sense to do in a different branch before merging it in - you don’t merge in half broken code. Squashing a large feature into one commit gets rid of any useful history that branch may have had.