They were aware of the runway closure and it was broadcast on the AWOS. Saving time has long been a Mantra at SW. It's built into their pay system where reducing block can increase pay. It's in the DNA of the airline.
Shortly after SW started operations at ATL I watched a Southwest jet pull out ahead of us from ramp 4 or 5 after being told to go behind us. I was moving along about 10 knots as there were 12 to 15 jets ahead of us. Ground gave them a short rebuke to which they replied they were sorry. They then said "We can take a intersection departure from J and are ready for a immediate"! After a pause ground control came up and said, "You're not from around here are you"?
Maybe it's time for a change in the pay system and agressive enforcement of the Boeing recommended taxi speeds of 10/15/30.