I cannot think about ANY other reasons to side with Minthara at this point of the story
The reason I came up with is "I'm a drow, I have no interest in whatever's going on with those tieflings, but I bumped into some goblins who gave me proper reverence. Then I find out another drow is leading them, I'm all in with this."
The dialog options did not make that rewarding in the slightest.
