The main reason is covid exposure and concerns about our health. So many students are quarantined or isolated right now, they will miss their original exam time(s) and then have to schedule a make-up exam session that will throw off any of their travel plans/parental pick ups. This is in addition to the tacit rule that make up exams tend to be harder than the standard exam, and that the stress of rescheduling flights, trips, and especially international travel will cause students to perform poorly.