Yes but often people just downvote stuff without saying anything to it. If they would put a comment there, it would at least be clear that they didnt read past the first line
if i dislike something, I don't always want to have to explain myself. sometimes i just dislike something and want to show it by a simple click. specially on mobile I don't want to write a comment each time. otherwise i would just stop voting completely instead of writing a comment each time i downvote something.
Sometimes others have already made a comment explaining your exact opinion of what you just downvoted, so instead of spamming more comments you can downvote one and upvote the other which explains your opinion.