I was wondering WHY the waitlist goes away?  Students who have been proudly at the 2nd position in the waitlist, and attending class hoping for a space to open up - suddenly can lose their chance because while someone else drops, someone who was never on the waitlist can "pounce" instead.  It feels almost like ebay sniping. 

I advise my students to be aware of this, and that I cannot make any guarantees

I know this is something decided by the registrar's office, but I don't understand the reason behind this.

(When "Drop" lasted a week or so more than "Add," I might sometimes accept a few extra, counting on some later drops, which normally happened.  Now it seems people are less likely to overload, planning to drop 1...I wouldn't mind this tighter drop/add period if the waitlist continued the entire time. )

Thanks!