this is true but it doesn't explain why;

this is the case because IM clients will often put a colon between the username and the message, so simply writing ) gives you "username : )". it then escaped simple IM clients and now the russosphere uses it even in the absence of the colon.

Your link is broken, try escaping your )

https://en.m.wiktionary.org/wiki/%29#Russian

edit: non-mobile link: https://en.wiktionary.org/wiki/)#Russian#Russian)