>>3132400I might have had a longer response in mind, but it might take me a while to research it, and I might take too long to reply, so, instead, I'll try to answer them on the spot.
I like monoeyes/cyclopes for the same reason I used to love elves. You mentioned them as vanilla, but, I think that is the charm. Elves have, more often than not, been drawn or characterized, especially in anime, as being humans with sharp ears. But we know there is more to them then that. We know that they are supposedly long-lived, even immortal. We know there is a massive mythology behind their existence, both in reality, and in the high fantasy that inspired people like Tolkien. To me, the monoeye is not "just" a monster girl. Its an entire mythological race, one that has permeated itself in both Japanese and Greek lore. The Greeks not only had Polyphemus, but also based the Brontes, the creators of Zeus's lightning bolts, as cyclopes. And the Japanese have the legend of both the one eyed monk, and the one eyed children.
The other is, I guess, a slight rebellion against those very tropes you mentioned. The cyclops is seen as brutish, yes. But when you see the anime monoeye, with her cute moe eye, you see something endearing. She's not some towering giant or brute, but something else. She can be like Sachi, a shy and timid girl who just wants to feel loved. She can be like Manako, who wants to feel acceptance. or she can be like Hitomi, who both yearns for romantic lvoe, but also has innate motherly instincts to all people around her. And I remember Iris from Ruby Gloom the most - she is a /co/ character, but, she represented a genki cyclops girl. Basically, in a moe style, a cyclops girl becomes something cute and endearing.
I'm sure there are more reasons I can think of, but that's a start. I'm sure other people have different reasons.
