You are usually looking at the iPhone, iPad or Macbook from angles that are not very flattering. The device is usually on a table or you are holding it in your hand so the end result is that you look fat with a double chin. By comparison a mirror is at eye level and you are facing it straight on.
Then you have the camera itself which isn't that great and depends a lot on having good lighting. As a test try facing your camera to the mirror and then compare how you look in it vs how you look on screen through the mirror.
Then you have the camera itself which isn't that great and depends a lot on having good lighting. As a test try facing your camera to the mirror and then compare how you look in it vs how you look on screen through the mirror.