Unfortunately, congestion at major airports is what happened when customers demanded more flights. Instead of a couple of flights a day from say MSP to SEA on a 767 or A330 there are now 5-6 flights a day with a mix of 739's and 757's. Or say MSP to JFK instead of one or two flights on a 757 there is now multiple using 717's or A319's. Those extra flights on every route add up quick.