They don't have enough coaches bro. That is the fact. but they are telling some other reasons... Already boatmail and kamban express has the coaches which are a decade old and not maintained properly. especially, Kamban sleeper coaches are not even maintained at MS. As soon as kamban reaches MS yard, they are detaching sleepers and attaching with Guruvayur express. and then GUV express brought up to pf 4 of MS...
the same happening in vice versa for kamban exp from GUV-MS exp... So the sleeper coaches in Kamban/Guruvayur never undergone primary maintenance... :(