Well I mean, they're aliens they created, why not just go nuts and give them double the amount of limbs or something? Maybe they talk about this on the GI video, can't watch it rn.
Wish Bioware's designers would just go all out with the (intelligent) alien designs. Different colored humanoids are so boring. ME1 had the right idea, but now that I think about it, I can't really remember seeing many Hanar around in the later games.
There are some technical complications actually. Asari, Turian and Human characters actually share the same base body model (and motion set) in previous games, for the reason of reducing workload on the game engine (and efforts needed for the development team). They are, literally, human characters with different color schemes and decorations. The same logic explains the lack of non-humanoids figures in game as well: the more interactions we have on the scene involving a Hanar, Elcor or Keeper, the more expensive man-hours Bioware have to spend on development, and the less frame rate we get playing on our machines.
I was hoping that in this generation additional capabilities from new consoles would help Bioware build a truly diversified universe where every species will receive fair treatment in the game no matter how many legs they have, however obviously I was wrong. They can't even get the facial expressions right.
P.S. I do not recall if Krogan uses the same base model in the game, though. And I believe that I read it somewhere that Volus takes their current form for the sake of easier development and better performance, too.