Bro , these trains ( Shipra /Chambal ) earlier used to travel via ALD & during that time their punctuality were horrible. These trains had to undergo rake reversals + Loco change at ALD which took huge time plus you know better about NCR controlling ( ALD - MGS ). Even Imperial ( Mumbai ) Mail also had the same condition . So , in order to decongest ALD & improve their punctuality these trains are now running via COI. Though punctuality has improved from past but still they runs late & then the ALD - BSB route also not that reliable due to single line section in many areas. So , its better to run this trains on their existing route .