Nobody does ballista but they still offer it. It is another option for people who want to do it. I just NPCed a ton of Colibri beaks because they were clogging up my inventory. Didn't AH them because I had 7 things on the AH already and other things are worth more. I would have much rather NPCed them to the Bonecrafting guild if someone could have bought them back and used them. Like I said, just another option for the junk we accumulate that people may still use but others aren't going to AH them because they make more off of them by NPCing them.