Why can't I choose Medium or High graphics?

On Android devices with 3 GB of memory or less, the game uses a special light mode so it doesn't freeze or close. In this mode graphics stay on Low, the picture is simpler, the draw distance is shorter and the game runs at 30 FPS in a match.

If you try to pick a higher level you'll see "Selected Graphics Level Unavailable". This mode can't be turned off.