To answer the OP's question ... on this January bid, here is the breakdown for the MD-88 NYC.

5 % of the trips were EWR
76 % of the trips were LGA
19 % of the trips were JFK

Of the LGA trips ... only 14 of 159 trips had the chance of being commutable on both ends. I drive to work, but most guys will tell you that our trips aren't commutable. So a 4 day trip is easily a 5 and more likely a 6 day trip.

Also, folks don't like having to cover 3 airports. If you are a commuter, that can be a real pain if you don't have a local car to drive. It really sucks when you're at your crashpad in Queens on reserve and you get called out to Newark. You just won a non-refundable $85 cab ride ... one way. Good times.