Why not only use a normal database?

At this point they should be, but they are in too deep and they are basically using the witnesses to create this information that is validated by posting key encryption.

Regardless, you are right, at this point the entire game can be taken off chain if they develop a way to let us sign transactions with our posting keys and send them directly to the server.

This is why the game shouldn't even have a centralized server to begin with. It should be run with a decentalized open-source nodes that all sync together just like a real blockchain would.

Easier said than done, I'm afraid.