Why do teacher recommendation letters sound the same?

RReaders in Stanford's admissions office could tell when a letter of recommendation had been built from a template, and at a big school the most popular teachers rarely have another option. Picture the teacher every senior wants. She is brilliant, generous and famous for her letters, and by October she has agreed to write for a large share of the class. In that office, a well-liked teacher at a big school might write fifty letters in a season, and some write well past a hundred. Nobody writes a hundred original letters, so even the most conscientious build a sturdy frame of praise into which each student's details are dropped, and the student whose letter was meant to set her apart ends up sounding like her classmates.