英语why not后面加什么MUST

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？