No grand story behind it they were made by Kampfkrebs who's been inactive for some time, Pahlava was the first one made because of TPC's art direction and insistence.

Saka came second because it was similar and Keravnos was fast to concept the idea. More factions were supposed to get intros like this but with Kampfkrebs away because of RL issues great intros will probably be made for EB2 from here onwards but who knows...