From what i found on the steam fourms:
http://steamcommunity.com/app/445220/discussions/0/135507855752966991/
Koonschi [developer] Feb 1 @ 8:33pm
Reasoning behind this was that I could develop for multiplayer immediately, and I didn't have to make a single- and a multiplayer version of the game. You can expect this to change in the near future, there will still be a server executable in the future, but the communication will no longer be done via networking.
It's been causing a lot of trouble (albeit for a small amount of players) but it's still an important issue that will be addressed very soon.