Mostly, those who use it, use it to find an answer to a (maybe) complicated question which they believe could be of good knowledge or act as a good information to other forum users, who might in turn want to appreciate the user by giving merit.
So considering the above, we know that those who use CHATGPT, just as the op have said, use it to make them appear more intelligent and knowledgeable than they original are, and this they do, all for nothing but to earn more merit in the forum, so if earning merits be the goal, indicating the real source of the information they are sharing might just be a goal damager for them, since the real essence of using Ai in the first place, which is to appear more intelligent than they truly are, is completely defeated.
Going back to the op, I think since the forum already have a rule against plagiarism, same rule can apply to those who use CHATGPT to make post, or better still, let the forum allow campaign managers to discipline those users involved in such an act.
Honestly, I don't know the motive why someone would use AI to create a post. Do they deliberately do this with the aim of creating high-quality content to gain merit? I don't think it's difficult if just comment, I wonder why there are people who like to use AI. Even though my post is not good, at least my writing represents what is in my head
For me using AI is like you are cheating as we all know that the post made by an AI from your account is not from your own perspective which means it's not acceptable for me cause it's look like you are plagiarizing some others opinion AI is made by human so technically speaking all the details delevered by an AI is from human too. So there's no point of using AI maybe it will make our task do faster but always remember the more you fast the more you failed.