Too many holidays might be a factor but I really doubt it's a large one. The bigger reason is you just don't delay a 20 year $10billion project for any holiday.
Some of the grunts might be disappointed but having worked on way less important things that were launched on holidays, I can guarantee anyone significantly involved in the project is just happy to see it get off the ground no matter what day. You have a good window for launch, you take it
