I was also surprised to see the dramatic spike on ports. I think what feline said was spot. In addition to those factors, it should be noted that masques was a pretty unpopular set. It was much less powerful than Saga, which it followed, and Saga also caused a big drop in player base due to the crazy combo meta and resulting bannings.

If you compare port to cradle while assuming that the current cradle costs are appropriate, the new port costs seem justifiable. While cradle has a much bigger casual appeal, port is much more common in competitive legacy decks. Port is also played in Lands, which I don't believe has been mentioned in this discussion.