The short answer is that it was expensive to host the multiplayer version, and it required a lot of work just keeping the site up to date (the game is the work of one person working in their spare time)
We were happy to continue this whilst there were enough players to make the game work, but we lost the traffic from the Chrome app and the game basically stopped working as a multiplayer game
As we can't guarantee that we will be able to find more players to get the game working again we have made the decision to switch to the Single Player version for now
Thanks to everyone who took part in playing the game, we are very happy that some folks enjoyed it and this was not an easy decision to make!