Well there has to be a real reason not something I make up in my head. Not that hard for blizzard to implement a proper way.
I definitely hard disagree with the number of Dungeons. 8 get old real fast even if it is just for 1 season but maybe experiencing it first hand will change my mind as in 8 new dungeons every 6-9 months. Legion was the best model for me as the new dungeons also made sense for patch reasons.