The answer is simple:
Discord.gg/rendog
Prior to the discord being established, this forum was the place to be, as it was the only way to communicate (one of). But as discord became available, and more rapidly used, there has been a steadily declining requirement for this forum, as discord is seen as a more instant form of communication, and also offers other forms of collaboration, for example, voice chatting.
So, I’m short, the reason not many people use these forums anymore, is simply because, there’s no need.