"Why do you not talk to anybody?"
Translation:तुम किसी से बात क्यों नहीं करते?
In this sentence as well, it is placed after the grammatical object. While बात करना can be considered a single verb or phrase depending on how you want to view it, it is actually a noun and a verb that mean "to do speaking" where करना is the "to do." This makes बात the (direct) object of the verb and thus कयों comes right after.
तुम क्यों किसी से बात नहीं करते - isn't that correct too...? I know it might not be the way it is said normally, but is it wrong grammatically? I see that quite a few people here are confused by the word order. It would be nice if a moderator/native speaker can explain.