Congratulation (again), JNOGaming!
I'd say more it's because there's so many of them. It's very well the most played mod, so there are many users writing AARs about it, which increases the chances the best AAR in general will be an AGoT AAR rather than a vanilla one.
Like I said in my Weekly Showcase post, I tried to move outside my personal area of interest but just didn't feel it would be genuine, or felt it would be a forced choice.
Speaking of which my nomiantion for WritAAR of the Week goes to...........
Wolves - aGoT House Stark AAR
Whilst it explores a scenario I'm sure a good majority of people have played, I like the intrigue of what Robb plans to do now, especially as he is now King in the North and has a Lannister up there with him.
However my main reason for this nomination is the writing is so good and I feel like I'm reading a book and feeling what the characters feel. I'd love to delve into this style more but don't feel like I have the time to do it and be consistent with my posts.