Because most players aren't savvy enough to realize how potent human build can be- to answer your initial question. Human Vers (even as a clicky) is uber, Human Imp Recovery is wow, two +1 stat enhancements is cool and the extra feat is a DREAM! In most cases, the extra feat is more valuable than a pidly +2 to a primary stat. Take a sorc, for example. A drow sorc can get to a 39 cha in today's game, while a human can get to 38. But the human gets an extra feat, human imp recovery (for self healing with umd), human versatility (to use heal scrolls in a pinch until you get your goggles made
), and another +1 to whatever dump stat you would like. Why roll a drow sorc when the sorcerer is already a feat-starved class as it is? AND take a -2 to con, a stat that is already weak for this class?! I dunno, my experience is that humans really make the best builds for many situations- but I'm NOT saying ALL. My main is a sorc, has a 38 cha and more hp's than any other sorc out there- I'm willing to wager. And I have an extra feat. For those of you who rely on kill counts to validate your char's? Always on top by a longshot- unless I'm with DrXav (16lvl CLR). (Yo, Xavvy) More importantly, however, I can step back and toss heal scrolls for +186 per cast and 100% accuracy WITHOUT hitting Human Versatility.
You're right- humans are not exceptionally represented in stormreach. The answer to 'why' is because of my initial statement, and maybe some players see a human in a fantasy adventure game as a little boring. *shrugs*