Thats because if the whole 24 coaches is sent to MTP, then that will burden up the MTP yard personels and the shunting dept as the arrival timing of this train is just 30-40 min ahead of the niligiri superfast express. So that means just as it arrives MTP platform, then within 20-25 min i.e by 0600hr the pf needs to be emptied for arrival of Niligiri superfast.
And i think 24 coacher would be a wastage in between CBE-MTP as maximum seats will be empty. Only tourists nd very few localites travel from CBE-MTP in such early hours. Thus reducing the coaches a bit at CBE will help a much.