In english, I would interpet the sentence "Why don't you come?" as an invitation where as I would interpret "Why aren't you coming?" as a question after having stated that I'm not going somewhere. Does "Varför kommer du inte" refer to the latter of these two meanings or both? If yes, does it depend on context to tell? If no, what is the most common way to say "why don't you come" in Swedish?
Wherefore art thou Romeo, i.e. Why are you a Capulet (or is it a Montague, forgotten me Shakespeare)
Because, apart from Shakespeare, nobody talks that way in English, anymore. Been out of fashion for more than 400 years.
First: in English when you want to make a question you should put the question word + v + s + obj your sentence was like this: question word + s +v+ obj and this is wrong in English.. Your second sentence is grammatically right but it's not in the right place.. When I ask you ( why are you not coming) it means that I want to know the reason.. But When I ask you ( why don't you come) It's like an invitation, a Suggestion, I hope you come or please come :)