Why didn't/couldn't Kabuto bring Orochimaru back?
Because Orochimaru was never dead. He was just sealed. Well, maybe "sealed" is not the right term. Every curse mark holds some a part of Orochimaru's chakra. And Sasuke reversed the cursed seal on Anko with the flesh from Kabuto to bring him back - 





This is from chapter 593.

PS: Almost same thing happened when Sasuke fought Itachi.