How is “why not” used?

In Stranger Than Paradise (1984), one line is: “- Yeah, we could. Why not? I don't know. - Yeah.”

Which movie is “why not” from?

The clip at the top of this page is from Stranger Than Paradise (1984).

- Yeah, we could. Why not? I don't know. - Yeah.

8 作品で登場 · 1 本目

used to ask why something is not so, was not done, or is not allowed; used to make or agree to a suggestion

567 本の映画に登場イディオムを再生

定義：Oxford Advanced Learner's Dictionary 第 9 版