So what? Adventurers don't have to be upper class (and I'm pretty sure most are not), they just have to not conform to cultural norms. "Upper class" is merely an exception that has been pointed out for certain very class based real world human societies.
Because I've only witness one halfling PC that wasn't "x killed all my family" or "I'm not like other halflings" or "I'm am the tiny terror!" in traditional settings.