“因为什么而高兴”在英语中可以说为 "be happy because of something"。
这个说法的来源可能源于人们希望表达因为什么事情而感到高兴的情绪。
一些例句：
I'm happy because of the good news. (我因为好消息而高兴。)
She's happy because of her recent promotion. (她因为最近的晋升而高兴。)
They're happy because of their recent engagement. (他们因为最近的订婚而高兴。)