왜 그랬을까

why did ... do that?

→ 왜
phrase Rare #24,132
why did ... do that? A reflective way to wonder about the reason for something someone did; the subject is often understood from context.
KO: 민수는 갑자기 왜 그랬을까?
EN: Why did Minsu suddenly do that?

다들 왜 그랬을까?

Why did everyone do that?

— 로우 (2017)

왜 그랬을까?

Why would that be?

— 퍼니 게임 (1997)

그건 왜 그랬을까?

Why was that so?

— 살인의 추억 (2003)

내가 왜 그랬을까?

Why did I do that?

— 벼랑 위의 포뇨 (2008)

그런데 왜 그랬을까?

But why did they do that?

— Kill Boksoon (2023)