"Why can't we just GET the Dark Soul?" ...What would you even do with it? Crush it to obtain numerous souls? Transpose it? Or would we throw it at people's faces for minimal damage? I really don't see what people expected. The important part of this DLC was revealing Gwyn's true face, and how he subjugated mankind and left them to rot under the guise of "protecting the Dark Soul." In actuality, he was imprisoning the Pygmy Lords along with the Dark Soul, knowing that if they ever realized their own might, they would easily overthrow Gwyn and the gods.
The reason we find the Blood of the Dark Soul is so that we can provide a haven for the forlorn, a destination for those seeking to escape the curse of the Undead and the inevitable fading of the First Flame. That's why the Painter needed to see fire--in order to give her world its own Flame, one originated from love, born of Ariandel's anguish toward the death of his surrogate daughter, Friede. Otherwise, the story would be left completely at a standstill, with no real resolution to speak of. While the world we've been protecting since DS1 may continue in its spiraling downfall, at least we've created a paradise free from serfdom for weary souls seeking rest, even if that world, too, must eventually fade with the First Flame.