Originally Posted by rkkwan

CO, like many other legacy airlines, are cutting domestic capacity this fall compared to last; and fall/winter already has lower capacity than summer. And CO are still receiving new aircraft. They have to be parked some place. Instead of parking some in the desert for the whole fall/winter, CO decides to just have long layovers of aircraft around the system.

As for why PDX more so than other airports, I have no idea.