the formal English we were taught in order to pass exams
「受験英語」は英語で 「exam English」や「the formal English we were taught in order to pass exams」といいます。
「受験英語が抜けていないからです。」は英語で「I can't let go of the formal English we were taught in order to pass exams」といいます。
ボキャブラリー
exam (entrance exams/examinations) = 受験
formal English = 正式な英語
we were taught = 教えられた
in order to = ~するために
pass exams = 試験に合格する
let go of = 抜ける