Maybe it's a matter of strength? I'm sure there are some people here who don't know how to fight, or don't have any sort of abilities where they come from. Or the opposite could be the case - some people are so powerful that the city might not last long if they could use the powers that they normally had, or powers that are at that level. [She can think of a few people back home who'd fit that description - like Gildarts. Or Natsu. Or herself. ...Okay, maybe those aren't the best examples - two out of three of those people are already here.]