怎么不 VERB (why didn't/haven't VERB) I have been facing a lot of examples of "why didn't/haven't VERB" in English translated as 怎么不 VERB. Why don't they use 没 VERB?

已经九点了，你怎么还不起床？（你怎么还没起床？）
你怎么不选一个更好的作文题？（你怎么没选一个更好的作文题？）

Thanks!
According to the book "Modern Chinese Grammar" (http://m.sanmin.com.tw/product/index/000225652), we can roughly distinguish:


不: this word is a negation that comes with the speaker's subjective feeling, which means that the speaker might think the other should have done something (for example in the first sentence, you should have already got up)
没: this word, however, is a negation which is more or less objective. That is to say, the fact that the other person did not wake up is noted.


To sum up, in both sentences, the contexts show very strong meanings that both speakers did not agree with what the others have not done, and therefore the negation word "不" was used. 

As a native speaker, I feel that using the negation word "不" is usually more powerful and that implies the relation with the other is more close. Hope this answer can give you some clues.