the fact is that it was such a huge undertaking that could not be completed in the life time of the fahro and it is stated how the pyramid would be started at the fahro's birth, and why the change to the valley of the kings ? if I remember rightly tutan kamons tomb had to be done in a hurry becuae he died young and that was not a pyramid, the change from the pyramids to the valley of kings could have been for lack of help or that they simply used structures already there and then moved on to the valley of kings when they filled the pyramids