I think the chat feature was an additional cost for the site and nobody was using it. There are plenty of free chat apps online and members are free to text each other. Maybe start a thread suggesting everyone who wants to chat install the same app or start a chat group or something along those lines. You could even include those details in your signature area or listed in your interests.
But, yeah, absolutely is the conversations in threads that muck everything up. That's what the PM system is for and some users choose to ignore that and ask favors or work out deal in the thread. All we can do is let those members know it's not helpful or respectful to do it. Let them know you don't like it and contact an admin. I've posted some threads where I clearly state people should PM me if interested in getting on a list, etc., and certain members (I will not name because I'll be accused of picking on them) still comment instead.
I've been a member here for over 2 years now. I've bred many species, given a lot of advice, but I get pretty bored answering the same questions and seeing photos of the same species again and again. The off topic forums are a way for me to keep an active presence even if there is nothing else interesting going on. I've met a lot of great people here and enjoy socializing with them regardless of the topic. The off topic forums are good for that and, like Mime454 said, filling out our view of the personalities we're dealing with. I've got to admit that some of the strongest connections I've made with members have nothing to do with mantids. I've gotten great technical advice on a range of subjects and some of those contacts came from off topic threads.