why do not you…一般不用,而用why do you not…
why do you not…,=Why not do sth?用来建议对方做某事.例如：
Why not go to visit your parents on weekend?=Why don't go to visit your parents on weekend?
(含义为：You'd better go to visit your parents on weekend.)
why aren't you able to…=why are you not able to…
以上情形说明否定问句要么不要分开,要么完全分开.
相信你能理解赞同吧!