You should really try Patna Mumbai Suvidha sometime (if fare is low ЁЯШВЁЯШВЁЯЩП), most Passengers are from intermediate stations not having Airports or Passengers with large amount of luggage as they'll face restrictions on Flights regarding those. Indian Railways is all about Minimum Number of Passengers traveling with Maximum Number of Luggage.
Now I travel to my Hometown Rewa from Pune via Mumbai in Allahabad Duronto. If I think of taking a flight from Rewa, I'd have to travel minimum 9 hours to reach Varanasi then another 30 minutes to 1 hour to reach LBS Airport at Babatpur, 2 hour before Check in and 2 hours for my journey- all of that considering the timings of my bus from Rewa and my...
more... flight from Varanasi match (which they normally don't), so I'm left with mainly train as an option. Something similar can be said for others too.
13 hours for flights vs 20 hours in train, I would happily take the train. ЁЯША