On the flip side you are putting all "humans" in the same bracket.

"Why are humans either starting wars, or enslaving other races?"

They're not. SOME humans are, but similarly how you ask the question why are they racist towards other races but not to their own races with different skin, you yourself have just lumped all humans together In Dragon Age sure there are some bad humans about, but they're also the main faction that fight against the Blight, so they are both the good guys and the bad guys.

I think it's rare that the main antagonist or protagonist in any book, film or story is anything other than human (or humanoid) if the choice is there simply because we can associate with these characters better and their lifestyles, culture and history generally mirror our own to an extent.