The reasons r :-
PNBE - NDLS route is comparatively faster than SPJ - NDLS route..
A pax from SPJ/MFP will reach NDLS in almost half the time through PNBE then through GKP...
As far as trains are concerned,i think both routes are given equal priority...
If...
more... premium trains like patna rajdhani,guwahati raj,sampoorna kranti,poorva,vikramsheela,BGP gr,JYG gr,brahamputra mail,magadh,ne and seemanchal runs through Patna then guwahati raj,vaishali,sapt kranti,shc gr,mfp gr,swatantrata senani,bihar sampark kranti,awadh assam,amrapali,sadbhavana,lichchvi,njp ndls... runs through MFP but i think no. of trains through both the routes for delhi must be increased...