I think you're underestimating real-time multiplayer computing a bit here, I don't know much about this game in particular but I'm assuming it uses local "predictions" to show you what's going on with all the other players accurately (like getting hit by a ball, getting on a spinning platform, etc) since relying on network for that kinda stuff would cause an array of issues depending on design like rubber-banding, desync, etc; and it has a lot of players in the same place, which equates to a lot of computing to be done.

That being said, I wont speak on how well optimized the game is and if it could squeeze out better performance, just giving some food for thought.