Because dwarves are pretty common fair among the Tolkenist fantasy and we all pretty much understand the tropes and concept of "The Dwarf". For the large part when it comes to "dwarf" what's often conjured - thanks in part to Tolkein and Disney's "Sleeping Beauty" - are men who live under the mountain or mine. They may also be independent, but who knows.

People understand this and the entire concept as been carried over so repeatedly through the fantasy genre it's pretty much cross-universe canon that the dwarven race are stout people of the underground who are made strong from a life of working metal, stone, and being rugged. And because it's familiar: we're comfortable. Same goes for elves, most often we keep recycling the same basic concept between stories we pretty much dug elves into being a single sort of arch-type; the only exception being Santa's midget helpers (like wise Dwarves have their different physical appearance as in the case of the Elder Scrolls with the dwarves - or Dunmer (SP?) - being the same physically as their above ground elven cousins).

And for people writing casually, and for people to write alongside them, and for the sake of the GM; it's comforting and easy to be and work a race that's familiar and with no real tricks up their sleeves. I've been in a few RPs where people have tried to make their own races, but they just often come off awkward and ill-crafted. Elves and Dwarves come readily pre-built and already understood, so the only changes needed are purely aesthetic choice.

EDIT - I'll also have to agree with Jester's point. As well as being familiar as I put, it may often be wish fulfillment. And I also often find people don't want to fill the role of a genocidal or homicidal maniac so may not touch things like Orcs so often, who are portrayed as less refined brutish, and violent people. I see a lot of moral one-upping a lot.

And then when people don't do it it's all in edgier than bismuth and honestly really goofy. And in these cases it seems most often to be often something like self-cynical with someone trying to prove how humans are evil by having a meniacal human. Which is certainly not unheard of for us, or any choice of fantasy race.

But maybe I'm just rambling here so whatever. Fuck it.


EDIT EDIT - Actually I think I basically missed the point of this thread and I would like to condemn writing well past midnight as a thing that can be done. But just replace the things before the previous edit or what not with "humen" and the point still stands: people like familiarity.