Because doing so would signal non conformity. Bryan Caplan has a book coming out soon on the signalling model of education here's notes from a course he teache

Because doing so would signal non conformity. Bryan Caplan has a book coming out soon on the signalling model of education here's notes from a course he teaches http://econfaculty.gmu.edu/bcaplan/e496.html http://econfaculty.gmu.edu/bcaplan/e496.html