Hello, explain why you do not have The Butcher's Circus free add-on in your store, AND WHEN TO WAIT FOR GOG?

the multiplayer dlc requires data collection for matchmaking and it depends on steamworks for it. i don't think they will ever bring it here. the dlc adds nothing to the single player experience and they actually messed up the single player game technically, adding stutter and several other problems that they are still fixing to this day.

also, all players are doing meta-based party compositions now. its kinda boring.

Yeah, the multiplayer is integrated with steamworks to make it work. They are using steams servers so for it to work you have to have steam installed and running with a legal copy of the game from steam. This is DRM.