There is a reason: BG and NWN are different games with a different design approach. Yeah, it’s really that simple.
Maybe you should think and talk about actual implementations of coop and MP in a game like KCD based on its very systems instead of just repeating yourself that other (and totally different) games included MP in the past.
Those games were designed from the start to have NPCs accompanying the main character. Multiplayer fit into the “module” style design of the chapters (or individual adventures if your playing through something a DM created for you and your friends). KCD isn’t designed around that six member party approach. It’s just going to be Henry and his dog. Occasionally a NPC will join Henry but only for specific quests and that NPC isn’t designed to be controlled by the player.
Comparing KCD to BG & NWN (which are great games in their own right) is comparing apples to freight trains.
If I were you I’d be pushing for an optional multiplayer mode for the tournament mode. There the implementation might be easier as it won’t alter the dynamic of the game’s story.
