Thank you for your input.
Maybe I am just tackling the problem from the wrong direction.
I really thought that people are willing to play NWN with someone without knowing the person in advance. That's obviously wrong for most people and some kind of networking is necessary. While I am willing and able to do that kind of stuff for my job or to find new real life friends, I neither have the time nor the will to network "just" to find someone to play a computer game with me. I just want to play it.
Sure, I understand that playing with someone you don't know has some risks that your playing styles are not compatible (role player vs. power gamer, dialogue reader vs. rusher, disagreements over difficulty settings and so on) but it takes only 10 minutes of chatting or maybe an hour of play to figure out if there is the possibility of further playing together or not, so I don't think this reason makes much sense. Especially if you take the fact into account that it extremely limits your choice of possible team-mates.
So basically the same things that always annoyed me about persistent worlds seems to affect this style of play as well: You have cliques of players who keep to themselves and make it hard and frustrating for the new players to become a part of the fun. I find it bad enough that economy and society work that way. Is it really necessary to copy that behavior for computer games?
There was this website. I think the name was "Neverwinter Connections". It made it possible to become part of a group without much networking first. You just sent an application with the backstory of your character and if you had put some effort in it, you could join the fun. Sadly, this website is gone. There has never been a try to establish an alternative. Now I understand why. People want to keep to themselves.