It's easier said than done, but all effort need to be made to complete outside "requirements" during the summers or holiday breaks. For reasons outside our control (a lot of places won't let you do electives til final year, etc.), this isn't always possible. At the moment, we don't really know what the situation is...
Of course, universities can't advocate US students going home for electives or USMLE study or interviews, because it can't be controlled. All students then would want to do something or other and there would be mass exodus. But on the other hand, it's not like we're leaving for an extended vacation...we're going home to do work.
So it's chance. They can try to enforce it and threaten us by saying attendance is mandatory, but at the moment, they don't have the means of enforcing it if we continue to pass our exams and prove to be competent doctors. It's not clinical work we're missing (which would be different), it's tutorials/lectures. This may change in the future. And it's not like we want to miss, it's just that sometimes it may be absolutely necessary in order to fulfill requirements for going back home, if we haven't been able to fulfill those requirements during the holidays (most of us have been studying/electives during summers too so where to fit everything in can be a problem).