The MAWs, and PIFs, and NHIEs aren’t set up as strictly CC only, so that gives the site some cover. If it happens that a guy gives another guy a CC in a thread that wasn’t set up to do just that, that was out of the administration’s control. In they allow a thread specifically designed for exchange of CCs between two people, then they have to take some responsibility for it happening. They don’t want to deal with any hassle that might occur because of it. It is their site, and their call.