Reason is clear. Kindly see the list of ALL trains going from CDG to KLK. You will be surprised to see that the Longest train as per coach count is this KLK shatabdi only.
So thats the reason why you can see this Shatabdi gets a Banker at CDG.
But yes , i am also hearing about bankers attached towards ropar lines also. I have never myself seen the same but as members are confirming the same , so may be bankers are now attached towards ropar also.