Maybe there's a compatibility issue with your device or your game version isn't updated.
There could be several reasons. It might be that you haven't fulfilled certain requirements within the game to unlock the story, like completing specific levels or achieving certain scores. Another possibility is that there's a problem with your game account or subscription status.
It could be that your internet connection is unstable, preventing you from accessing the story mode. Or, there might be some technical glitches in the game itself that need to be fixed by the developers.