Interesting design decision to leave the app icon intact. Many app developers have updated their icons and “flattened them”. Now the Instagram icon is the one icon that’s jarring on my home screen. A company who’s one app becomes their whole identity has an great challenge with those radical redesigns, that I would assume will come from Apple quite regular moving forward.
Facebook now owns Instagram and perhaps the reason for not redesigning the icon is that Facebook tries very hard keep the Instagram independent. For now.