Simple fact Mathstagandha is a favourite in KR whereas VSG PNBE is an SWR train and KR don't want to run much of SWR trains on their tracks nor want their trains to be extended to SWR(VSG) even if public will benefit by it. This train was forced by Ex RM Lalu Prasad Ji in his tenure on KR route so they won't give it much priority.
I bet that if this train was MAO PNBE SF or even Karmali PNBE SF it would have definitely got a good priority in KR.
But...
more... again this weekly is even trolled in CR too. Lot of scheduled overtakes in CR too especially in Patna Vasco direction.
SWR don't care about it too as it doesn't serve SWR apart from VSG.
I even said it before here on IRI and even today I say this should be degraded to a normal M/E as even the actual average speed is below 55.
No zone would for its speed up so better to degrade to M/E so passengers are not cheated.