I think you’re misunderstanding me. I didn’t say he drops them 2 weeks into the semester. He drops them after getting access to the syllabi and meeting the professors. His schedule is generally set by the 2nd day of classes. Not all the students decide that quickly though. At his school it’s common for students to change courses for the first week or two of classes. That’s the way the system is set up.
I don’t think it’s a student’s responsibility to make sure other students get the classes they want though. They’re each responsible for getting the education that’s best for them. That’s why the drop/add period exists. A student who picks up a course someone else dropped probably also has to drop a course to fit it in, and maybe that course was something another student was hoping to get. They’re all trying courses out and making adjustments.
My son’s college doesn’t seem to have a huge problem with closed out classes. The upperclassmen register first, so the classes taught by the most popular professors or the most popular electives may fill up, but the underclassmen just put those off until it’s their turn to register first. There are multiple sections of the courses required for the majors, so it’s not a problem getting into those either. I can see it might be a problem at smaller schools, but registration at the smaller schools I’m familiar with is handled differently.