英語why not後面加什麼MUST

Why not have the dish of the day?

為什麼不吃今天的精選菜？

Why not write to her?

為什麼不給她寫信呢？

Why not tell her you're quitting and have done with it?

為什麼不告訴她你打算辭職，儘快把這件事了結了呢？

I didn't want a part in the play, then I thought ─ stuff it ─ why not?

我本來沒想在劇中扮演角色，然後又一想——管它呢——幹嗎不演？

Why not spoil yourself with a weekend in a top hotel?

為什麼不到頂級飯店度個週末，讓自己享受享受呢？