I might as well rephrase it to see if we can get a proper response from zoythrus, why was the app photo changed? Any particular reason?
So, there are 3 main reasons:
We ran a study on app icons, and noticed that downloads increased by 20% when this icon was the one representing the game on the App Store/Google Play.
The app icon was changed to match the store icon, since the store icon was so popular (as per reason 1). This was to reduce confusion.
We wanted to change it.