The simple answer is dlc, especially the expansion pass standard of the modern industry, is absurdly easier to get a return on investment in than an actual new game.Because it's going to cost them virtually nothing to do.
Literally a single player game mode, some skins, and another skill tree - really all things that should be an "update" and not "more DLC" but what do I know? It sure all sounds like stuff that was probably supposed to be in at launch but didn't finish in time that the skeleton crew is trying to shit out for $$$.
It isn't even interesting like SP1 (which had new areas/quests/items/etc).
90%+ of the work is already done, just by virtue of being add-ons to a base game, and they can charge $30-40 for an additional 2 or 3 hours of content on top of a 10 hour $60 game. Even if a fraction of a fraction of the install base purchases, they've more than made back the money they spent barely paying their borderline slave labor code monkeys.