How much does it cost to completely craft a new universe? It certainly is much easier to start with a known archetype and go from there.
Developer to writers: Follow the architype, humans are naive, elfs and wizards are too smart for their own good, dwarfs are evil
Developer to artist: You draw elves in the forest, you draw humans in the village, you draw orcs covered in mud
Starcraft (1998) was given as an example of breaking from this tradition. It is an amazing game, but just as unoriginal as the others. Please entertain me.
An advanced race who are governed from a golden pyramid, have energy weapons, travel through circular gates that connect across planets, have luminous eyes, need to mine minerals to survive and want to kill the people of earth. Is that the Protoss? Or is it Stargate the movie (1994)?
http://www.youtube.com/watch?v=hWC3-VzDGMY&NR=1
Slimy space aliens that are led by their queen which covers their home area with slime, hatch from eggs and can infect humans. Is that Zerg? Or Aliens the movie (Alien 1979, Aliens 1986)?
http://www.youtube.com/watch?v=bNhARS02rfU&feature=related
Original writing is hard, time consuming and expensive. It often doesn't pay for developers and doesn't review well. How often do reviews pan games for using well know archetypes if they can execute well. In fact players are comfortable with well known archetypes because they are different enough to be fresh while familiar enough to be approachable.