In Mass Effect, as the protagonist, you've always been the most important and exceptional person in the story - even the most important/exceptional person in the galaxy. It just makes logical sense to me that the most exceptional person in the galaxy ought to look
exceptional too - at least, from a story standpoint. From a realistic standpoint, they could look like whatever the hell they want - but in stories, the most important people look
important to draw attention to them and put them in the spotlight. They're what you want the audience looking at.
Not only that, but typically in stories, the bad guys are uglier than the good guys. There's a reason for this: you need some quick way for the viewers to be able to recognize someone as bad, typically with the exception of A. horror, or B. seductresses.
There are a lot
of commonly-used tropes on this. Here's some of the most common ones:
Face of an angel, mind of a demon
- Horror trope for disguising the villian (or making them more horrific). Ace Attorney, Undertale's main character, Skyrim's Babette to name a few. Mostly used in movies because it typically takes longer to develop the full effect.
Evil is sexy
- Also goes into what characters wear, as well as how they look - there's a tendency for evil female villains to be not only attractive but rather slutty in a teasing sort of way. Metal Gear series, Final Fantasy series, or - oh, look - Mass Effect. Remember Beneziah and Aria?
Evil makes you ugly
- If a good character turns bad, they typically begin to look rather ugly to emphasize the change. Palpatine and Anakin, anyone? How about Voldemort? Star Wars: Knights of the Old Republic, Castlevania: Lord of Shadows are other examples. Oh - and how about Mass Effect 2? Remember how the scars were tied in with the Paragon/Renegade system? Mass Effect 1 had Saren become monstrous when Sovereign took over. Typically, though, this is more often used in movies, literature, and (especially) comics.
Beauty equals goodness
- a double-sided trope: Good characters look good, bad characters look bad. This is all
through the Mass Effect games - remember how hideous the Collectors were? Good characters typically look better. Actually you can apply this to almost anything
, with the exception of the top two tropes above. It's virtually universal. The purer and more "good" a character is, the better they'll look. In stories, appearance relates personality. (Note: the main exception here is if this is supposed to come as a surprise, or make you hate them. For example of the latter, Gaston in Beauty and the Beast.)
tl;dr: there's a reason main characters look good in games, and a large part of it is story-based. Mass Effect's writers used to understand that... but I suppose they have new ones now that don't quite know what they're doing.