For the simple fact that Mass Effect has the advantage of being a better medium -- video games where the fan has more interaction than in a show or a movie -- and that the player can put themselves into the character and play it how THEY want to. I also enjoy the universe, timeline and storyline a hell of a lot more.
In Star Trek and Star Wars, humans run everything. In Mass Effect, humans are insignificant in the grand scheme of things(much like how the universe really works) and they're trying to find themselves in the galactic community. Bring in the hopelessness of the Reapers coming in to wipe out organic life which is what humans are 'made for,' and it creates all kinds of messages that Star Trek and Star Wars couldn't even hope to comprehend.