I heard someone say Orochimaru doesn't make money for Kishi so he decided to get rid of him. Considering hes a main villain, his fanbase was not as huge as expected of a main villain.
Well this is for those who said so; Allow me to show otherwise:
Kakashi's fanbase >> Oro's
Jiraya's fanbase >>>> Oro's
Itachi's fanbase >>>>> Oro's
So Oro is not as much appreciated yet Kishi decided to keep him around while getting rid of those characters with massive fanbase. What does this tell us? Kishi doesn't give a f*ck about money! As long as hes doing as he wishes he'll succeed, because hes that kind of author.
I guess the main point is; Kishimoto doesn't base his story on the expectations from people. He just wants to create a good story.