Correct, I noticed the feature recently too. I'd imagine it's anti-spam (or at least anti-lurk?) but it's not like you can comment without an account.
I don't see a good enough reason to toggle that unless you're expecting a non-user to leak it to another platform to make fun of you (e.g. Lemmy) and obviously we're proof enough that it isn't much of a deterrent, lol.
This is a way to slightly make a block work better to keep away from stalkers. Yes, a stalker can create another account. But it does add an additional small speed bump.
It’s a way to dip their toe into being closed off. Right now it’s a “user choice” so some people can slowly build the wall while feeling good about “blocking AI scrapers” (they’ll get around it no problem) or “blocking stalkers” (they’ll get around it no problem) or “blocking [next week’s bogeyman]” and all of a sudden everyone has to make an account to interact with the website but it was oRgAnIc™