In Star Trek Online, I'm generally satisfied with a simple "to blow up the bad guys." Not asking for much there.
With World of Warcraft, I'll settle for "it's pretty here, the fights are fun, and I can smash stuff."
With Star Wars: The Old Republic, though, you have to really motivate the experience. When you spend so much effort on a game establishing it as a story-driven MMO, you need to have a legitimate reason for grouping up to tackle a task, and for making the call to action appealing to each player.
I spent some time yesterday in the group finder tool, just hammering out flashpoints and thinking about the content I was playing through.
