It's a self-defeating cycle. The lack of any dev presence or response on this forum is, I believe, one of the main reasons for everyone leaving. When you have a game forum, people visit, primarily, because they hope to be able to give their opinions on the game, and they do that with the hopes that they can make a difference and help to bring about positive changes.
I've been doing this many years and I have never heard one word from any developer, aside from in the carefully curated update videos. If they answer questions in those it is only the questions they have particularly chosen (or perhaps made up) in order to talk about what they want to. I am not belittling the valiant work that mods and CMs past and present do to try to bridge that gap, but ultimately I don't think it makes any difference. I genuinely believe that no game dev has ever even visited this forum to read a thread.
So, for the most part that is why people walk away. Sure, there is, and has been, some good community spirit. That is great, but if that is all people were seeking then they would seek it on a different type of website.
And then, purely crunching the data, they see that there is not much traffic or engagement, so their answer is to shut down the forums and move it onto a different platform. There is a certain inevitability about it. And will it fare any better over there? Possibly. Temporarily. But if their policy on interacting with the player base remains the same then people will walk away from that too.
I am possibly covering some really old ground, and apologies for sidetracking this thread, but I am in a whimsical mood.