How is “why ever” used?

In Pride & Prejudice (2005), one line is: “Why ever not?”

Which movie is “why ever” from?

The clip at the top of this page is from Pride & Prejudice (2005).

Why ever not?

6 作品で登場 · 1 本目

イディオム

used in questions to mean'why', expressing surprise

6 本の映画に登場

used in questions to mean'why', expressing surprise
Why ever didn't you tell us before?

定義：Oxford Advanced Learner's Dictionary 第 9 版