This is misleading ..Currently Gaya has very limited no of flights and that too only to Delhi and 2 International Destinations mostly catering to Buddhist tourists. The Flight options that you've shared are all Connecting ones. Notice the duration, 14H - 21Hrs ... In this duration Trains reach Delhi / Mumbai from Gaya ... I think currently Gaya only has 1-2 flights daily to DEL on an average and not 14 and 15 as you have wrongly derived.