Increasing AC fares more is the reason behind this. I too traveled from patna to Delhi on 25th by flight bcoz the cost of AC 2 in suvidha express was 100 rupees more costlier than the flight ticket.
In long route above 1000 km Air fare is cheap. But its not much applicable to Delhi-Mumbai or kolkata. Unfortunately railways do research on these routes only. So they dont know about other routes it seems.
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