Please add "why aren't you dancing?" As the correct form! There have been many times when "aren't" was not accepted as the correct answer... I wonder why...
What's wrong with "Why you don't dance?"
Word order. It's a question, so it should be 'why don't you dance' or 'why do you not dance'
Nie mam ochoty tańczyć, nie proszę pana, dziś nie ma tańca.