Imagine an actual DnD campaign where the DM only allows the player to initiated the NPC interaction to speak and use their abilities..
It would be much more fun for all players if any character present in the conversation (i.e. PC + followers for any player who's listening in) unlocked their corresponding dialogue options and were allowed to use their abilities. E.g. letting the cleric use their medicine check instead of just being a spectator. If this makes the game too easy or something, just bump up the difficulties of the skill checks to compensate
Found some old posts from the beta where players were complaining about lack of teamwork outside of combat in co-op and Larian answered with something along the lines of that they tried it but it turned out to be too difficult to implement.