What does HOI4 have that CK2, EU4, and even Stellaris don't have? Can anyone guess it?
Since HOI4 released, it has had 3 DLC released for it, with a combined price of $45. Time since base game was released, 897 days. Average time between release so far? 299 days and counting. If they released MTG 14/12/2018, that would be 4 DLC, $65, 921 days, 230 days average between DLC.
Stellaris has had 5 (6*) DLC released for it, with a combined price of $70 ($90*). Days since release of base game, 941 (925*) Average time between release so far? 185 (157*) days and counting. *Everything in parenthesis is adjusted for Megacorp.
EU4, 14 DLC, $215, 1925 days, average time between release is 138 days.
CK2, 15 DLC, $183, 2338 days, average time between release is 156 days.
I counted all DLC listed as such on the wiki. No flavor, music packs. No pre-order bonus, skins, etc.
Disclaimer: I won't pretend to be a worthy judge of the actual value of all of this DLC, and the free patches that came with them.
Why? Your guess is as good as mine as to why HOI4 post release development seems so slow. It could be, as alluded to in the title, it simply isn't priority, which means less developers. It could be because they don't see much profit in DLC for HOI. Maybe they are so stretched between supporting three games, developing one plus whatever else they are up to that HOI4 simply drew the short stick. If you want a greedy corporate answer, maybe it is because they already got our money for DLC.
Perhaps it is something as simple simple as coding and getting things right for HOI4 is much harder than previous games? Seems incongruous to me though.