There is no comparison of Patna to any other city of Bihar, but one thing people often deny is that the whole crowd from Patna Airport or Patna station doesn't belongs only to Patna. Atleast 30% of crowd comes from other city to Patna to catch trains/flights.
Banglore/Pune/Mumbai/Hyderabad/Chennai/Cochin/Surat have limited connection to other cities of Bihar, so people travel to Patna to catch trains/flights increasing footfall/revenue of Patna.