I apologize if I'm repeating some other responses.
There are many variables that go into the equation. The other night runway 08/26 was listed as closed in the ATIS. We had an alternate and had to carry extra fuel. We used the magic words to use Runway 08, but the tower said no dice due to overnight construction. This caused us to be weight restricted. We made it work but had to crunch some numbers and consider using a headwind credit. I'm not sure about the performance on a 737-900 but I think it seats about 20ish fewer passengers. Also I don't know the flight loads, was the AA flight full? What about the DAL flight? As few as 10 empty seats could have made the difference in making it to BOS VS flying to CLT.
Why fly to CLT? Simple. It's a large hub and crew base with flights to Boston. There are almost always extra ground crews available to handle flights. Let's say the flight was dispatched to stop for fuel at an airport just north or south of the weather in the upper Midwest. There's a good chance everyone at the station would have gone home for the night. Or if their shifts had just started they are only properly staffed to work the flights that go out early that morning. Now you could potentially run into a ground delay waiting to be parked and for fuel. The last piece of this puzzle is the crew, are they properly rested for a 2 leg redeye with a possibly lengthy fuel stop? Now the crew is fatigued at an airport that's not a crew base and no flights to Boston, so you're waiting for a crew to be deadheaded in from the nearest crew base. Even worse would be the airline cancels your flight so you have to be rebooked to connect through a hub and then on to your final destination.