> This practice makes even less sense when we make PRs that once merged are squashed into one commit
Up until the point of merging, other developers reviewing the PR can see your development path, and optionally examine individual commits. In GitHub at least, these individual commits usually make their way into the squashed commit's comments as a bulleted list of changes (after some cleanup), which encourages better final commit messages in general.
I examine commits regularly, sometimes going way back in time. Maybe not daily, but pretty frequently. Usually, I'm trying to figure out why something is the way it is (so I know if it can be changed, removed, or whatever), and a clean history makes this exponentially easier.
Up until the point of merging, other developers reviewing the PR can see your development path, and optionally examine individual commits. In GitHub at least, these individual commits usually make their way into the squashed commit's comments as a bulleted list of changes (after some cleanup), which encourages better final commit messages in general.