Because it is a topic for a separate game or may be several, and not for the DLCs.
Really!?
Soviet-Afghan or do you mean the other conflicts?
I'd love a proper game about the Soviet-Afghan war! Despite the fact that, as Flashburn pointed out it was rather one sided on paper, there is still plenty of evidence and material for some great battles.
"Bear went over the mountain" and it's sister (brother?) book "Other side of the mountain" contain dozens of battle reports alone, and I'm sure there are many many more out there to be created.
I did enjoy the Soviet-Afghan campaign in SABOW but it felt very difficult and at times dull, from the position of the tank only...
Anyway enough rambling, this is about Zhalanashkol, and personally I'll be looking forward to it - While it's a small border conflict it could be quite fun as you'd have very limited resources and as it'll be closely modelled on the real conflict (down to names of commanders) we can try to recreate it perfectly and go the other extreme and give it a completely different outcome.
Careful planning and a new way of fighting would be required (one would imagine).
Will have to see what content is available and how it compares to the price tag though - At the end of the day I have a lot of GTOS to play so I'll have to see if I can justify buying another DLC before finishing the others. :P