IMHO, a part of it is that it's getting to be around time for PDX to start working on CKIII. CKII is 6 years old, which is an eternity when it comes to games. This is really starting to show in many aspects. CKII is still fun and PDX could certainly still pump out a few DLC, but soon "blob die repeat" is going to mean that most people would rather just hit up PUBG or EU4 than CKII. Plus, CKII is starting to have a rigidity problem. In CKII, religions do the same things, the same cultures show up. Yes, Reformed Slavic England is funny, but after your 4th Reformed Pagan game you realize that Reformed Pagans really aren't all that different from each other. Things like the Miaphysite Church literally have no flavor except for some extremely minor things and even then they get plowed down by the Muslims usually within the first 100 years of the game, completely bypassing the fact that Christian Africa was a huge part of West African history. A part of what CKII needs is a revamp with a significantly more dynamic religion and culture system. No 2 games should be the same after you gain enough power. If you're playing as the King of Lombardy and conquer North Africa, instead of North Africa turning Italian/Lombard, perhaps it should turn Berbero-Lombard or something like that in between. Heresies should go from "random things you convert to when you wanna holy war other Christians/Muslims" but something that if you leave it alone long enough it could have real teeth. Furthermore, they should be more dynamic in that perhaps they have random traits generated on the ascension of a "heresiarch" rebel leader. It can be a real problem when that heresy you left alone because you were to busy tumbling with your inbred horse-sister suddenly spawns a 50k rebel stack intent on turning your realm into a Heresiarch theocracy.
Just, overall, while CKII itself in the form it is in now is nearing the end of it's capabilities, in the future, a CKIII game with a new engine that is really up to date with what is possible now could be truly magnificent.
Just, overall, while CKII itself in the form it is in now is nearing the end of it's capabilities, in the future, a CKIII game with a new engine that is really up to date with what is possible now could be truly magnificent.