Most schools don’t have an indoor space big enough for all the graduates and guests.
My graduation was in the school football stadium, and there was no limit on attendance. In later years, it was decided that outdoor graduation was too hot (or rainy), and they started holding them in the city convention center. This required issuing limited numbers of tickets to each graduate for his family/guests.
Michelle could issue each student an Obama-phone (as a graduation present) and give a remote address from the comfort of the White House. Everyone would be happy.
Most schools don’t have an indoor space big enough for mooche's big @$$. Fixed your comment.