When Soifon and Yoruichi are fighting each other in the soul society and Soifon tells the story of why she hates Yoruichi so much, she asks Yoruichi why she left, and Yoruichi never answers her, but the fight just ends and they go work together to stop Captain Aizen and the others from getting away.

Can anyone tell me why Yoruichi left? and why she didn't answer Soifon when she asked her the same question?