MYS-SBC is just 3 hr journey. so 3A/ 2A will be very costly and no one will pay high fares. But, Cholan is comparitively longer run train. They can have 2S for all sleeper coaches and run 3A/ 2A AC coaches with CC fare (no bedrolls need to be provided).
Every one travelling in the train get some fringe benefit. This can improve occupancy also. Instead of paying 3A fare of Rs. 660, one can travel by paying around Rs. 500. To TJ/ MV, it will be still less.