Even connectivity also matters. Mathabhanga and Mekhliganj aubdivision are also located in Bengal and they also need to travel till Kolkata which is their state capital. This train was extended in this route for serving these two subdivisions. Moreover the Dhupguri route also doesn't jave important city ot town between Jalpaiguri Road and New Cooch Behar
As I said in my previous comment, the arrangement of trains from cities of North Bengal to Kolkata is just perfect and there isin't any need to alter it