It hasn’t
Not necessarily. These schools also practice holistic admissions, so the choices will be evaluated in context. If there is a valid reason for the choice (e.g. following the British curriculum) than that choice will be viewed differently from an invalid reason. In my mind, decisions which will get a closer scrutiny include:
• I don’t like the subject/I like another subject more
• I don’t like the teacher/the teacher does not teach
• I don’t want to wreck my GPA