YOU SAID:

we didn't do it because it was easy, but because it was hard.

INTO JAPANESE

簡単だったので、それはしませんでしたが、難しいからです。

BACK INTO ENGLISH

I didn't do it because it was easy, but it was difficult.

INTO JAPANESE

簡単だったのでやらなかったが、難しい。

BACK INTO ENGLISH

I didn't do it because it was easy, but it was difficult.