Because sometimes we all have to learn how to receive criticism gracefully. There are many ways you can react when you get feedback on your novel. You can have poise and grace and act profession or you can fight whoever is giving the feedback nail and tooth.
You NEED a critique partner in order to write a book, whether it be a beta reader or your editor. Even if you don’t agree with what they may say you need to take their opinion into account and adjust the book accordingly.