That’s my reaction to most of these, too.
I actually have an idea, and in my mind it’s not that sexy. I theorize they appear either fleshy and reptilian or turtle-like.
That having been said, I would totally make a Shepard to romance Wrex if he were an option, and I found Garm (of the Blood Pack) oddly attractive.
Not most types, which I suspect might surprise you since I run a porn blog which indiscriminately posts anything Mass Effect.
(Yes, I know I haven’t posted anything in a while. My apologies. I should be getting some up soon.)
The only porn I really like is porn of characters from my fandoms which is respectful, not too dirty, and is true to the characters and who they are as people (or aliens, or elves, or whatever).
Oni has proven himself over and over again to be the best at that, though even he isn’t perfect.
It’s easier to show than tell. My favourite pieces are all tagged “stamp of approval.” That’s the easiest place to look.
Thanks for the question, anon!