The fans are probably a part of the consideration, I would think. Once you do the math to remove the TV and movie stars that get shown during the games, there’s around 35,000 on up in the stadium. Plus, unlike throwing a court down or getting ice ready, there’s the field to deal with, making sure it’s ready to go.
And really, with the NBA and NHL, isn’t there usually an additional buffer day or two between the last possible game 7 and the start of the championship round? Maybe there isn’t, but I think there is at least a hangover day, a travel day, and a day before.