I'm pulling it from the understanding that game developers focus on the most liked games, and most popular.
We are getting a HOI IV, and got an EU IV. Only reason there isn't a CK III or IV is because CK II is so golden as is, why change what works? They are probably afraid of fudging up CK III, and with the depth of the mods of CK II might as well let it keep it's glorious prestige.
But.. Vic II? No real new expansions, hardly looked at by paradox and while sure there is a player based, and sure would be great to have a VIC III, doesn't seem to be getting nearly as much attention by paradox. Reason? same reason every developer has to favor other game titles.. whats most popular?
further proof? look at the forum posts.
Crusader Kings II
Discussions:
77.977
Messages:
1.279.302
Europa Universalis IV
Discussions:
64.180
Messages:
1.017.837
Vic II
Discussions:
25.592
Messages:
406.882
Vic II has less than double the amount of either game. So yes, I do believe the community speaks for itself, quite literally of which is the most favorite.
I could be wrong.. but I doubt it.