Cause Azure Phoenix may given mercy to anypony but also give to fair share like cheat to let's Celestia's win. Azure Phoenix is more powerful than Celestia but he's didn't want anypony get mad for him to doing beat her so he's used a fair as mortal ways such as no Mystic Magic.
I sincerely he would do that. But I'm about to add some serious twist to this one. And by the way, if you have the idea for Friendship's Heart of Destiny Chapter 9 or any of Mystic Season 5 Episodes, let me know. I may include Flare Tiger or her family into it.