Hi there, dev here!
Glad you guys like our game! We have put a lot of love into it and we're ecstatic that people are enjoying it so much. SO! Let's talk multiplayer options because it's something we've been asked about before. Networked multiplayer of any sort, online or LAN, is a complex beast. Basically, the choice to add networked multiplayer boils down to a couple things: design philosophy, and network latency (lag).
The amount of development time and resources it takes to implement heavily depends on the style of game. A turn-based game, for example, is fairly trivial because network latency of like half a second is irrelevant when you're just taking turns. For a game like ClusterPuck, however, it's very fast-paced and involves a lot of interacting physics objects, so half a second of network latency just destroys the game. Latency is an unavoidable fact in network play, and it's no easy task to accommodate for it in a twitch-based indie game (just ask the devs of TowerFall or Sportsfriends!), and so we decided early on that this was going to be a local-only game.
The good part about this is that it informed our design goals, and helped us craft the game around being the best local co-op experience we could muster. Knowing that this would be a game played with friends on a couch, we could build the game such that it would enhance the social atmosphere of playing with your buds and make use of the best elements that local play brings to the table. Those intense, split-second moments where your friend makes a goal shot with 2 seconds left on the clock, and you miss the catch by mere pixels, is not only much more satisfying when you can immediately turn to your friend and scream horrible things in his or her face, but isn't really possible with 0.25 seconds of network latency.
Of course, despite this we realize that this style of play might not be the best match for every player; some people have friends who live far away, or some people might not have multiple controllers on hand, so in such cases it might just not be the game for them.
We do really appreciate you taking the time to download our game and check it out! If you have any other comments or questions for us, we would be happy to answer.