It's all about zonal railway's preference. WR wouldn't want their loco to be attached to different zonal train. Because CR is already giving KYN locos to their train. It is all a business. You wouldn't want your neighbor to use your car, when he already has his car available. That's how all this things work. Until all the routes don't get electrified, they will not try to change the process that is going on right now.