Why, because they used it as a "bad guy protagonist"'s name in this game?
Or because it's been 33+ years since it was invented and you have certain preconceptions about names in the universe?
Because it has "killer" in the name?
What kind of a name is "Biggs DARKlighter"?
If he were a Sith, as we all know, he'd have "DARTH' in his name (according to the new rules Lucas made up in the mid 1990's).
Think about it though...
Doesn't make a real difference, does it?
Anyhow, it isn't a big deal. The names switch all over the place. I mean, the "Dianongahs" were at one time a name for a group of people (even good guys too if memory serves), not garbage eating tentacle monsters. Even General Vader was just an ordinary official (like General Veers) before he was turned into a Sith Lord. Prince Valorum was a Sith Lord, and then, 20 odd years later was turned into an ordinary politician (though the original character sketch of Valorum eventually became Palpatine the Emperor).