At this point, I think it's pretty obvious that these cycles track with a subliminal fear of U.S. Presidencies that reach their term limits.
There's this sort of instinctual dry-up, right before the eight-year mark on an incumbent president, sort of like geese flying south for the winter. No one says anything to one another, but the angle of the sun changes, the summer weather is gone, and all the birds hit the road at the same time.
Regardless of the parties and there representation in whichever offices, and under whatever titles, everyone knows that different people will be sitting in different chairs when the dust settles, for some, there will be a new-car smell, and for others there will be painful hours stepping through a debugger, converting data from one format to another. Either you'll be comfortable while the bugs shake out, or you'll be in for a cold winter in a drafty house, but since the immediate future is up in the air, everyone stocks up for a harsh winter.