My reason for having applied to your school is because...
I would like to be admitted to your school, because...
I applied to your school, because...
ご質問ありがとうございます。
①
"My reason for having applied to your school is because..."=「貴校を志願した理由は...」
②
"I would like to be admitted to your school, because..."=「私は貴校に合格したいのは、なぜかというと...」
③
"I applied to your school, because..."=「私は貴校に志願しました。なぜかというと...」
ご参考に!