Local train exist in low count at non metro places and increasing these counts will affect mainline SF/EXP speed. Stoppages in PNBE route for most trains are as good as like passenger/fast passenger (Farakka, Magadh, Shramjeevi, Vibhuti, Punjab Mail, Janta etc). And as you said: More stoppage will invite short journey WT travelers. DDU-Gaya dont have any much of day-time multi stoppage trains as compared to DDU-PNBE!!