The reason for this is unitraction policy. Being a weekly train its difficult for arranging e-loco links from intermediate trip sheds, or coming up with some kind of LSA with another train, also the idling time of the diesel locos will be more if the loco is changed at say itarsi, hence the diesel locos are used, same as the chennai- shirdi express. In future when the entire stretch is electrified then we might see either GTL shed or BSL take over the e-loco link