Sorry if I don't know much of the lore or if this question has been asked before. But per the title: why do we even have the Underdark? A wilderness area full of 1 single quest. Is the Underdark just there for lore? What is the point of going there?

I didn't mind when the expansion first came out, but now that I have TR'd a few times/characters I find myself annoyed more than excited every time I have to make my way from the Kings Forest to the Drow City of Sschindylryn.