Because diesel zindabad tha, zindabad hai aur zindabad rahega :p
Jk, electric loco ka shayaad availability nahi rahega as many trains are being operated towards north, same being the issue with e loco crew.
There are other issues, most notably with height of OHE and top of tanker being quite close and no earthing being done between tanker body and rails, but if that was the main issue they would have taken non electrified route outwards.