I'd find it likely that at least one reason he doesn't use an outside source is those users are not registered to This site. Thereby lowering the number of registered users.
Also losing access to chat logs. The records kept on this site, and the previous chats, aided in banning people, catching trolls, scams or even illegal activities.
Some people may not feel comfortable going off site, as well. Or may be unhappy to join CC only to realize they have to join a separate site in order to chat.
Just a few considerations I've thought of as to why he may choose not to go elsewhere for chats.