Probably because they're worried about keeping two providers in sync throughout the entire world, or they don't have a DNS wizard on staff. I don't see why syn

Probably because they're worried about keeping two providers in sync throughout the entire world, or they don't have a DNS wizard on staff. I don't see why sync would be a huge problem; these days moving services usually involves slowly draining active connections from the old addresses while new connections go to the new address. If it takes a day for all the clients to move to the new address then fine, the migration just takes longer.