Everyone does, because a) you get to control the messaging to the user, and b) once they've declined the OS prompt, you can never re-do in your app, whereas if

Everyone does, because a) you get to control the messaging to the user, and b) once they've declined the OS prompt, you can never re-do in your app, whereas if they decline your own prompt, you can ask them again whenever you like, like when you know they've just had a positive experience.