I noticed that the Civ VI Fanbase has shrunk a lot lately. There are much fewer Discussions / interactions / Engagement than there used to be some Months ago, especially since the release of Humankind.
Well, personally I think most of the topics have been discussed. Civfanatics have always been busy talking about which leader next, which systems next, why leader X works or doesn't, who they like to see. Now that there is a definite conclusion, most of these options have a limit to how much they can be discussed.
I see a lot of topics opened that could just be a new post in an already existing topic (someone finding X that looks a bit like X in Civ, doesn't need its own thread), and most threads veer off-topic amazingly fast, and always under the guise of "Well, I know this is off-topic, but..." or "But we are going off-topic so let's go back to the thread [now that I've had my say I can tell you all to stop talking]". It's almost always either discussion whether [thing in history] was like X or wasn't like X, or someone making a remark, someone expanding on that remark, and then you get a whole subthread about whether remark was true/funny/whatever.
I mean, even here, you already see people adding to their message what doesn't work in Civ, what they think will happen in the next franchise. It's low in number, and might stay that way, but I wouldn't be surprised if this thread eventually goes off-topic too, which brings me back to my opening: most things have been discussed, so that's why you see might see the same topics crop up, and consequently see less activity here.
As for why people play the game less (if that's even true?) I side with Pokiehl and Zaarin. I've been playing it since launch, have clocked in about 3000 hours, and the game has gained such a transparency that I find myself just clicking the turns away on autopilot.