1. because eBay itself figures out the actual international shipping that includes DC and also whatever the customs or duty fees to buyer are and all are included in amount buyer is presented with at cehckout - no additional fees or costs are allowed.
2. and 3. GSP does not protect a seller from any claim of Not As described by international seller. That's the downside that you have to live with for being exempt from delivery confirmation only as far as Kentucky. Damage does not mean the package was damaged in transit - could simply mean item is not as decribed - and nothing eBay can or will do for you if teh actrual package itself was not "damaged" in transit from Kentucky to buyer.
You can be exempt fro SNAD if you skip GSP and buyer uses (their choice) a freight forwarder, in fact any buyer that has an item forwarded (even if they moved across town and USPS or CanadaPost is forwarding all their mail) is supposed to lose any and all Buyer Protection - but it does not always work like policy claims it to.