The game doesn't offer any provable fairness, furthermore it is client side, for it to work with the website it needs to be server side with the game sending an AJAX request to the server for the coordinate of the next square after every "move", this could potentially make the game less responsive. We could send Websocket requests but then it would be even messier. Did you consider that people will inevitable build bots to play the game instead of them and collect 0.4BTC every time?