Why can't you do that?
Why can't you do that?
何でやってみないの?
なぜいけないの?
Why don't you do that?
Oh no! it is not nearly finished.
なぜいけないか。
Why can't that be prevented?
Why can't you participate in that?
Why is it that you won't do that right away?
Why didn't you wake me up?