Pretty much everybody prioritizes their CR with their character's partner and then maybe 2-3 others, less because they are cliquey and more because they are either slow players or have the game as their second or third game. It wouldn't mean much in a bigger game, but in this case it means you're SOL and might as well just drop if you can't find a new "good" partner for your character soon.

That said, there are some gems who tag out a lot and will happily let anybody who wants in on plot too.