Depends.. If the studio actually made this content after the game went Gold
Are you aware it takes 2 to 4 weeks for a "gold" to become a release on shelves? Meanwhile, putting a DLC online takes less than a day. 4 weeks means a lot of work can be done. Doubly so when that's the last four weeks Most of the shit that goes into "day 1 dlc" is shit that's no longer about to be finished around the gold deadline, but might just make it in a couple of weeks more. Hence, a launch day online content. If it can also be sold for moar jewgoldz, well, all the better, the joke's on the suckers.
Next you'll say the CK2 DLCs are being invented on the fly strictly beginning on a day a previous DLC is uploaded on steam, not planned ahead for months, with all kinds of preliminary milestones being done in advance. "Okay guys, we have just finished testing our Peasant Baronies DLC while all our artists and all coders and designers save for one were twiddling their thumbs spitting into ceiling for a month. Let's now gather and brainstorm the next one, now that Peasant Baronies is finally released, we are morally permitted to work on the next thing which otherwise we would have been obliged to include into Peasant Baronies. Testers, proceed to the thumb-twiddling zone, we're taking next month prototyping". Yeah, right.