Ugly Aliens?

well, for the same reason we sometimes have trouble identifying animals without unique indetifying features we can easily use (such as tail spots on whales, etc, but even then thats what scientists use) and we have our own subtle identifying features, aliens would have identifying features of thuer own that they can easily observe but we can't observe very well. That and the designers can't really make thousands of different individual pics for the same species.

lol i like your last point Lazy basterds

I want some real bloodsucking reptillians in the game so I can conquer earth and play David Icke's dreams.

Have you ever tried Ascendancy? Not only are there no Humans, some of the races are so completely bizarre that if we really did encounter them we'd be hard pressed to identify them as life, much less intelligent life, or figure out how to communicate with them.