Often times a trainer will name the same rider on both halves of an entry. This can be for several reasons. The trainer might plan on only running one horse and scratching the other or both horses were ridden by the same jockey last time and the trainer is going to allow the rider to choose which one he/she would like to ride. Without seeing the form, did the named jockey ride both horses last time they ran? If so, it is just a courtesy . Once the rider and agent have told the trainer which one they will ride, the trainer will name another rider on the open horse if both will start. There are probably a couple of other reasons but one of those two are usually the case.
Hope that helps.
Hope that helps.