It always needs to be pointed out that every sequel's release is compared to a more realized and expanded version of its predecessor. Civ 7 has not had 2 expansions and DLCs yet or a long chain of patches that focus on its dialing in its mechanics that are unique to its design. But it is being compared to every version that has. Familiar features are missing, causing disappointment if you enjoyed those features and expectations are being met with unexpected results as no one's expectations are 100% spot on because none of us are psychics. Some are pleasantly surprised, and others are not.
Part of all of this comes down to: there really were just fewer people talking about past games in this same franchise. Consider the fact that on these very forums the General Discussion for Civ VII, released one month ago, has 257,000 posts, while Civ VI, released almost a decade ago, has 424,000.
This is a pretty good metric, I think. I cross referenced steam forums to find that WAY more discussion happens here than on Steam about any given installment of Civ. (By hundreds of thousands more) If you are a Civ fan, you will come across people talking about civfanatics and find your way here. This comment intrigued me so I figured I would look a bit more into it also. I added up all of the messages (not threads) for everything
except Technical Support (As it would give "credit" of popularity to any version that had more problems for people.) and
Creation & Customization. (As that will be highly influenced by which version offered more modding tools.)
For anyone curious, Civ 4 (released source code for modders) wins by a landslide with 1.6M. Then Civ 3 & 5 tie with just over almost 700k and almost 600k respectively.
The threads where people just simply had a desire to discuss the game with others online in different ways are where all the other categories fall into.
Civ 3 - 1,194,900 (Over 24 years) (49,787.5 posts/year average)
Civ 4 - 2,222,800 (Over 20 years) (111,140 posts/year average)
Civ 5 - 918,100 (Over 15 years) (61,206.7 posts/year average)
Civ 6 - 466,700 (Just over 8 years) (58,337.5 posts/year average)
Civ 7 - ~68,500 (6 months) (11,416.7 posts/month)
What I find interesting about this statistic is that it suggests that this community has shrank. That may not be true, but activity has certainly declined. I was not very active on these forums in 5&6's life cycles. Plus, it is still worth noting the modability of 3&4 vs 5&6 even though I left those figures out, since a very active mod community will drive activity up in the community as a whole. You could argue something like reddit but that is hard to track and I am not seeing big numbers of discussion anywhere online.
It is impressive the amount of activity Civ 7 has generated in such a short window. A corrected error has made it less impressive, and more standard. Time will show how much staying power it has. Those numbers could theoretically trickle off now that launch has passed, or they could shoot up with updates.