Why disable Commenting?

I think there are plenty of reasons. Bullying is definitely one - people might have been subjected to it and chose to shut the doors to the possibility of a repeat, or they might be turning off commenting as a preemptive measure.

Another is anxiety. It's one thing to put creations on the gallery for others to see and a whole another to get comments (good and bad) and deal with those. Not everyone is built to be able to deal with that. It may seem easy and awesome to want to encourage someone or send praise (and thank you everyone who does that) but for some people, it comes with the feeling of obligation to respond to those comments which can be hard. (I've had a few comments on mine and I inevitably a) don't know whether I should or shouldn't reply since you can't @ users on there to notify them, b) felt guilty when I didn't. It's complicated.

But I'm sure there are some people who just don't want the comments, don't care for them, don't want the notifications (since it's only a "everything on or everything off" option on the gallery).

The reporting tool on the gallery also needs a major overhaul, honestly. It's been misused way too much.