The TRPs are low...so people already dont watch it...if they showed Promo just one or two days before VD's entry...it would hardly attract more audience for the main episode...maybe later but not VD's entry epi...which I think the makers want...cuz it will be a turning point.
And also this way ensures people watch a few epis before entry and get a gist of related events that led upto that special twist...or they wont be able to relate na...
Moreover releasing promo and articles a week before may be AS and teams way of assuring people that its not gonna be all negative...an interesting twist is promised and a few pertinent details leaked to assure us that all is gonna be well soon. So we can tune in to watch these epis in a better mind frame.