Everyone has to care about something.
Well, it's hardly generalising. Fact is, if Slavs were such a huge deal, then this would be marketed as Slav dlc, not Norse or anything else. All the art work is Norse, all the diaries have stuff about Norse, there has to be a reason for this other than it's a Swedish company. I'll give you a clue as to the reason, people know what Vikings are, they are interested in Vikings. You are in the minority if you are all about Slavic stuff.
Of course. But the fact is, you are wrong to think that "nobody" cares about Slavs unless they have a nationalist interest in doing so. So you were generalising to say "no one is really too interested in Slavs all that much, other than those whose national pride has been hurt by the lack of information". That is not true. I am also hardly the only non-Slav to show some interest on the topic (and many other people have mentioned Romuva and West African paganism who have no nationalist interest, as well).
But I'm glad you'll be buying the dlc for more than just viking stuff because I'm sure paradox has put a lot of effort into other areas of the dlc, even if those areas haven't been marketed as much as the things that the majority of people want to see.
I don't think they did at all. If they'd put a lot of effort in differentiating the other pagan faiths, they would have said so, and they would happily respond to queries about Slavic pagans with "They have a ton of cool unique features we just haven't had time to talk about!". I think the fact we've been told Suomenko, Romuva and Slavic pagans have one unique festival each, and been told nothing at all about West African paganism, is in fact a pretty accurate representation of how much work has been put into them. Paradox wouldn't answer questions about the differences between Sunnis and Shiites for the Sword of Islam DLC either, and there turned out to be a really good reason they didn't (they are functionally identical). They didn't talk about how anything other than Italian merchant republics worked for the Republic DLC, because the Republic DLC is only designed to replicate Italian merchant republics, is bland for other types of European republics, and flat-out doesn't work right for non-Christian republics. They didn't talk about content other than the Hordes, Chinese factions and Japanese system for Divine Wind, because aside from a simple unification there was nothing new in Divine Wind for India or Southeast Asia. And so on and so forth.
Don't get me wrong. I understand that vox populi, marketing reasons and personal interest made them make the DLC 90% Norse content (including pushing back the start date for the primary reason of making the Norse religion that is functionally a dead letter in 1066 important again), and don't blame them for doing so, exactly. But pretending they showered effort they're just not telling us about on things they've conspicuously not mentioned (which is pretty much everything other than Norse and a sprinkling of Zoroastrian and Tengrii features) flies in the face of pretty much every other time this has happened. A lot of people are cool with this because that's all they care about too, and there's nothing wrong with that. A lot of people were cool about there never being a pagan DLC because all they care about and want to play are Christian feudal lords, and there's nothing wrong with that either.
But the chances there's going to be any other DLC to try and accurately represent Slavic pagans, or anything at all related to that large, populous and historically important area of Europe are pretty fricking slim, so why wouldn't people who do care about it be concerned and vocalise their disappointment that it's being shoved in the "all those other guys" dustbin yet again? Zoroastrian fans got extra content and attention because they wouldn't shut up about Zoroastrians. Why should people who want more content for Slavs (or Baltic pagans, or whatever) shut up about their area of interest? How else is Paradox supposed to know that people, contrary to what you said, actually care?
