It may be that they want the track configuration on Guardians to be kept a secret, whereas Tron is already a known entity. To me it seems like building the building first, then the coaster seems more logical. I would imagine if a roof beam dropped on the coaster track it would be a lot more expensive and time consuming to fix, but that's my logic on it...Why is this build like Rock'n Rollercoaster, first the spaghetti-coaster than the box, and Guardians at Epcot they build first the box, than the spaghetti-coaster?
I think building the spaghetti-coaster first would be the easiest option.