I haven't read the topic so I don't know if it was said but seriously the answer is girls. All of the girls that I know who play games like KotOR or ME are in love with Carth. One of them referred to Kaiden as Carth 2. They have to have that character so that the girl Shepards have someone to relate to and pick. As cool as Garrus is, I'm sure that most of them would prefer ending up with a human. It's the same reason that Ashley and Miranda exist
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skull