この場合、次のような言い方ができます。
ーWhy did you go to all that trouble?
「なんでわざわざそんなことするの?」
to go to all that trouble で「わざわざ…する」
ーWhy did you walk down there on purpose where there are so many puddles?
「なんでわざわざ水たまりがいっぱいあるところを歩くの?」
on purpose 「わざわざ・わざと」を使っても表現できます。
ーWhy would you intentionally say something like that to make the other person angry?
「なんでわざわざ相手を怒らせるようなことを言うの?」
intentionally「故意に・意図的に」を使っても言えます。
ご参考まで!
Why do you intentionally walk on the road where there are puddles?
Why do you purposely choose words that would anger someone?
Why do you do something that would bring about bad results?
ご質問ありがとうございます。
① "Why do you intentionally walk on the road where there are puddles?"=「なぜ水たまりがある道をわざわざ歩くの?」
② "Why do you purposely choose words that would anger someone?"=「なぜ誰かを怒らせる言葉をあえて選ぶの?」
③ "Why do you do something that would bring about bad results?"=「悪い結果を及ぼすことをなぜするの?」
ご参考までに。