Such percentage of migrant workers must be very little who can afford flight fares. If the employer is paying the same once a year i can understand. For flights to sustain over a long period of time there needs to be regular occupancy. Earlier few years ago, Jet did have services and one more flight operator ( i think it was Spice Jet) had services between Kochi-Kolkata.
Unfortunately both had to discontinue due to poor occupancy. Hopefully this time they must be having some good data before them to start flights !! . We will have to wait and watch