Considering the way they announced it last time with literally no warning, put a trailer up online and left it to die and then invited no media sites to play the game for review, it absolutely does need more marketing.
There would be millions of Inquisition players, particularly PS4 players, who have forgotten that JoH even exists. The way they handled the announcement of the DLC was awful.
My feeling is that they didn't make a big deal about it due to the exclusivity thing. They knew that many PS4 and last-gen console players would be annoyed that they couldn't get their hands on the DLC. Hyping it up would have only made it worse.
I also think that since the DLC was made at or near the time of DAI's release and much of the content would be the same- large area with lots of fetch quests and not much story- which was a criticism of DAI, they didn't want to over-hyoe it for that reason as well.
That's just my feeling though. And I'm super annoyed Hakkon won't be coming out till the *end* of May, but whatev.