Why can't I switch sections of a class, or switch classes after the second week of class?

Switching sections is considered a Drop/Add.  "Free adds" (you go to computer enrollment and add any course for which you are eligible and which is open) occur during the first week of class.  After that, its up to the discretion of the department/professor.  Many feel that if you missed the first couple of weeks of class that you will not be able to catch up, or it may disrupt on going group activities.