For a long time no loco changes were made because of the DC-traction on the CR/WR tracks. The respective zones did not want to have 2 loco changes ( one at PNVL and one at BRC ). Even later on, when the DC-AC conversion work was going on, with the WR route having been converted to AC and the CR portion still on DC, , again it would have required two loco changes ( one change to WCAM at PNVL and another change to WAP at BRC).
Moreover, all trains going towards BRC from PNVL were only weeklies and bi-weeklies ( TVC raj has the highest frequency at tri-weekly). So overall CR didn't feel that it was worth...
more... investing in a trip shed at PNVL for a few weekly trains. Freight trains have many nearby yards where loco changes can be carried out and even IR in general, prefers having freights running with EMD's frequently using EMD's on electrified routes as well.
With the Konkan electrification sanctioned now, again an ETS at PNVL might get delayed.