She's not "random villager 7 that was standing by the stables."
Luckily, a lot of her backstory has been exposed over the years. She's one of the protectors of the secrets of Grayskull and trained Man-At-Arms (along with Dekker).
I'm just going to write this one off as another case of Mattel not wanting to make something fans want. Like...Keldor's half swords... We're still waiting on those, by the way.
Re: Gygor. Illumina has a lot more history than Gygor. The only difference is that he's older. Illumina is much more well known. Illumina is like Brad Pitt and Gygor would be like Ryan Kelley. Don't know who Ryan Kelley is? Exactly. Fans first learned of Gygor from Roger Sweet's book, which had a couple sentences about him. Then we saw a picture a year before the Gygor figure came out, I think. That's all.
Illumina also has a LOT more parts re-use than Gygor did.