Probably preparations are not yet fully made regarding the allotment of locos which will haul them as a regular link...And I think the trains bound to Assam and Tripura will continue with E2E D-Loco from HWH/SDAH/KOAA itself... Freight services with E-Loco have started though as per some local RFs of the region..But it's just my idea the senior and experienced members may give u the proper reasons...