Why disable Commenting?

Agree with you both @Taoron and @Cupid. While it annoys me personally when someone's commenting is off (especially, if they have commented on my creations or wall first), I do also understand, if someone doesn't want comments on their wall. Not only does it slows down rest of the Gallery and game, if there are tons of comments on your wall, but it's a time taking matter to individually delete comments and to thank and comment back. Since ppl typically expect polite behavior such as replying or thanking back, not being able to do so can give excessive feeling of guilt and/or discomfort.

Another matter entirely are those who use Gallery sharing as their game world save cloud/backup because shared content will remain in Gallery, if your hard-drive breaks down and you loose everything. The content that was only uploaded/saved in your library (catalog) will be lost.

There are plenty of other reasons as well like trolling, bullying, spamming etc. and for a young person it can be as destructive as typical bullying in school is. Of course there are also those who don't know they've turned it off or maybe (for a young player) their parent has turned it off.... Just my thoughts of the matter :)