As on any other SE site, comments to explain down votes are not mandatory. And the two discussions you've linked (as well as several others on various meta sites) list both the pros and cons of enforcing, encouraging or nudging users to comment in case of down votes. That's why users with rep below 2k get displayed a nudge/short note when down voting (which still doesn't make it mandatory though).
OTOH I agree that users would benefit from having down votes explained (in a fashion helping them to improve their posts). But that's up to the individual applying the down vote.
Also - remember that votes are designed to be issued against posts and without regard to the user - so if you can focus on the content of the post and improve it or be kind - that works best for the site and especially so when the poster is a new user.