Because those are the characters that people want to use! I find it a little bit odd that you asked three questions in succession, and in each one you referred to certain characters as Jason’s pet characters. As opposed to your pet characters. It’s right and proper that Jason and any other writer write about the characters that most interest them. You make it sound like a cheat or a conspiracy or something–but it really isn’t. And you don’t want Jason writing about your pet characters if he’s not interested, because all he’s going to do is a lousy job, and then you’re going to be even more frustrated.