Why are you doing this? I just felt like running.

VOA: standard.other

You say, well, why are you doing something so foolish?

你会说，你为什么在做那么傻的事啊？

麻省理工公开课 - 固态化学导论课程节选

if you are doing something that you hate and you are not happy, why bother?

如果你做自己讨厌的事情，就会不高兴，何必呢？

怡人的的汉普斯特德 - SpeakingMax英语口语达人