McKibben gives a terrific run-down of the history of our traditions and how many of them were perhaps suitable to the people in those times and places. "Over-the-top" makes sense if your life is laborious and rather removed from all the stimuli we face. (Here's a stat from reading unrelated many years ago: we process in one DAY mentally what our ancestors at the turn of the last century 1800s-->1900s processed in a YEAR.)
Plus, their notions of "huge" fall amazingly shy of all our dreams of Christmas. He gives ideas for homemade gifts in his little book, and the biggest focus is on what our needs actually are around holidays: we need a season of peace. We're made for connection to nature, each other and the divine. So he hopes our traditions and time spent around Christmas reflect those needs. Christmas is an antidote to the onslaught we face daily, when our days feel less holy. I think he published this book in 1998--how much more true it seems to ring!