Why not use PocketFlow's flow for the game's internal state machine

I'm just curious of why the PocketFlow's flow and node can not be used for implementing the game's internal state machine, telling which stage of the game it currently stays? won't it be easier to define nodes for these game stages and a flow as state machine instead of having so many if-clauses in the app.py? at least better readability than the current app.py with almost 2000 code lines :)