为什么不是 be disappointed about 而是 in或with?

disappointed with / in somebody 对某人感到失望
My father never showed if he wasdisappointed with / in me.

爸爸从未表现出是不是对我失望。

disappointedwith / at / about something 对某事失望

You must be pretydisappointedwith / at / about your exam results.

你对我们的考试成绩肯定挺失望吧。