It is an ideal terminal point for trains. Due to it's location, there is very little scope for trains to run 'through' SGNR. There are shorter routes for trains going to Bathinda, and passing trains can go directly from Suratgarh to Bathida instead of taking a round-about way through SGNR. Thus it doesn't have mush passing traffic and it will be easier for IR to handle originating trains from here, compared to more major stations like JP or Bikaner.
Effectively it lets IR tackle two problems with a single train.
There...
more... are many large towns/cities which have a lot of originating traffic. The demand from/to these places is constantly increasing and IR needs to run more trains to these places to keep up with the demand.
But running more trains requires more space for parking/platforms at these stations, and it is difficult to improve those facilities frequently. So, the solution is to cover as many routes as possible with as few trains as possible.
So they usually end up extending the trains to some station beyond the main city where they can manage the rakes more easily.