当番委員のペアが決まった日なのよ？他のみんなはお祝いしてるのに、何が悲しくて、そんな、さびれ果てたとこへ行かなきゃならないの？
What does 何が悲しくて mean here? It seems to mean "What's so sad that we have to go there?" but I feel like I'm missing something.
「何が悲しくて～～しなければならない（のか）」
is an idiomatic expression used to describe the unreasonableness, unfairness, outrageousness, etc. of the situation where one must unwillingly perform an action.
Thus, a literal translation of the expression will not work well because the expression grammatically looks as if it meant "because something is sad, one needs to ~~~".
The English counterparts I could think of would be:
"Why the heck am I supposed to ~~~?" or
”What good does it do if (I) ~~~?”
This expression, therefore, differs in meaning from 「何が悲しいって」 or 「何が悲しいかって」, both of which do mean what they literally mean -- "what is sad is that ~~."
Hope this helps.
