I think there is a lot of idiosyncracy to the whole process as well. Sometimes, poi might be not taking new students or fit is just not that perfect. I also am not sure how foreign schools are generally viewed. One thing you are coming from a known university, but if it is something people have never heard of, I feel like it might have negative impact.
given that they do not require writing sample from all applicants it is reasonable to assume that they place more value on grades, gre and lors. I would advise you to look over big threads in this forum on application. I found them very useful.