You are not addressing eBay here, but members like yourself.
Simple Delivery was announced last October that it was coming to all Private Sellers, and warnings that existing items may be automatically switched over in the coming months. The latest Announcement, see eBay News top left of this forum page, explains if any remaining listings are still showing Custom Postage these will automatically be switched over to SD on August 6th.
It's not liked by many, look down this Discussion Board, to see the many threads from disgruntled members, but it's here to stay.
@fiftyfindsboutique