Because if we create a party of 4, we can't even bring any origin characters into the party to trigger dialogues like Lae'zel and Zorru, or Shadowheart at the statue, or Wyll and the gobbo captain.
You mean you want to create 4 customs characters in multiplayer and see content from origin characters at the same time, right?[/quote]
Yes. I create 4 custom characters using Multiplayer mode, and I have no open slot to add Shadowheart to gain more of her story, or Lae'zel, or anyone. If I have 4 custom characters, I miss tons of fun stuff in the game. At least with party of 6, I could add 2 origin characters at a time and still gain content.
Besides, again, my main point is WHY NOT? If the functionality already exists, and players really want it, why not give it to us? What harm would it do to allow us 6 party instead of 4?