I dont know why that was, but it happens.

我也不知道他们为什么这么做，但这的确发生了。

youdao

Your face before me though I dont know why.

不知为何，你的脸庞浮现在我的眼前。

youdao

I dont know why he is late, he might have had an accident.

我不知道他为何迟到，可能遇上了事故。

youdao

Ms. LENA HORNE (Entertainer): (Singing) Dont know why there's no sun up in the sky.

NPR: Entertainer Lena Horne Dies At Age 92