Why not have the dish of the day?
为什么不吃今天的精选菜？
Why not write to her?
为什么不给她写信呢？
Why not tell her you're quitting and have done with it?
为什么不告诉她你打算辞职，尽快把这件事了结了呢？
I didn't want a part in the play, then I thought ─ stuff it ─ why not?
我本来没想在剧中扮演角色，然后又一想——管它呢——干吗不演？
Why not spoil yourself with a weekend in a top hotel?
为什么不到顶级饭店度个周末，让自己享受享受呢？