なぜならbecause, the reason is, if you want to know why

私(わたし)は数学(すうがく)が嫌(きら)いだ。なぜなら計算(けいさん)が苦手(にがて)だからだ。

I hate math. The reason being that I'm not good at calculation.

もう離婚(りこん)しようと思(おも)う。なぜならもう愛(あい)を感(かん)じないから…。

I think I'm getting a divorce now. Because I don't feel any love anymore...

犬(いぬ)は少(すこ)しも動(うご)かなかった。なぜならあまりにお腹(なか)が空(す)いていたからだ。

The dog didn't move an inch. The reason being he was too hungry.

母(はは)は弟(おとうと)に対(たい)してかなり優(やさ)しい。なぜなら弟(おとうと)はまだわんぱくな３歳(さんさい)だからだ。

My mother is very kind to my brother. Because he's still just a rambunctious 3 year old.

やっとこのブラック企業(きぎょう)を辞(や)める決断(けつだん)が出来(でき)た。なぜならこの企業(きぎょう)にいる事(こと)でどれだけ健康(けんこう)に被害(ひがい)が出(で)ているかを理解(りかい)したからだ。

I finally made the decision to quit this black company. Because I realized how much damage was being done to my health by being in this company.
#Note 'black company' in Japan refers to a company that typically exploits its workers and has a poor working environment and/or work-life balance.'