the women in DS are middle-eastern by geographical happenstance and, several of them, genetics.
I don't think DS represents the cultural and social reality of women in the middle east accurately in any time of history, nor do we aim to do so, however "inspired" we might be.
They are women in a post-apocalyptic dystopian future world setting that have dug up an even older model of society and are mixing and matching according to what has trickled down to them through the ages and adversities.
I've seen a fair bit of women in different AVNs having ethnic traits, outfits and skintone for pretty much any colour in the rainbow and ethnicity under the sun without, in most cases, focussing on representing that part of the world. (there are a few, yes, but indeed a minority)
What makes a woman actually middle eastern is the setting of the game and said setting reflecting a middle eastern society and system of values... in other words, she has to actually show behaviours and values corresponding to what we can call at least an approximation to middle eastern representation... and the characters around her have to share in this cultural bedrock, otherwise she's just standing out like a horse in a herd of sheep.
The fact that this type of character is severely underrepresented is easy to understand. most people not from that region of the world wouldn't know how to represent it accurately and most likely aren't even that interested in doing so.
After all, it's not what they are familiar with.
Those who could do this type of setting justice and might have an interest in doing so and seeing their "world" getting the AVN treatment, probably live in countries where the production and/or perusal of pornographic material is, at the very least, problematic if not downright dangerous for them.