The rate of success of a group RPs tend to be dramatically lower than one-on-one RPs due to the pressure and lack of control when dealing with more than two people. Collaborating with an individual pouring their interest in an RP is a bite of relief in comparison to collaborating with 5-10 people, especially when one of them ends up quitting due to lack of time on their hands. This hits especially hard when the character they are controlling is vital to the plot, or rather, contributes to the plot significantly. Though of course, said character can end up being controlled by others, the GM themselves, or abruptly "dying" in the story.
At least... that's what I've been seeing most of the time.
Eh. I disagree. With 1x1's, you
have to really click with that one other person -- and if you don't, then it's going to fall apart in no time. And if
anyone drops out, then it's dead, and there's no way to salvage it.
But with groups, you don't
have to only RP with one other person. You can interact with lots of different people and get a better flow of ideas going. If one player isn't giving you enough to work with, you can shift your attention to someone else. If
one character becomes a wallflower, then it's not like the entire RP stagnates, because you still have lots of other players who are still actively moving the story forward. And if one person drops out, then it's still possible for everyone else to move forward.
That's why I prefer groups, anyway. One of the reasons I couldn't get into 1x1's was because I just couldn't find a partner that met all my needs -- and even when I did, the story still felt like it was stagnating after no time at all. I just need more ideas to work with than just what one person can offer. And when that
one interaction fails, the whole RP dies. With groups, I have a lot more flexibility.