Perhaps 1) Khufu needed to align/site his pyramid with/on something natural or manmade on the ground and 2) didn't expect anybody else to build on the Plateau.
Point made. And IMO that point is.....all we can do is give it our best guess as to why which one was built where. There just isn't enough info for a solid conclusion, yet. Building on bedrock probably was a major factor, if not the determining factor as to where they were built. But since none of us can lay our hands on a survey of the area, we can't know the lay of the bedrock.
Regarding your point of Djedfre, that could be convincing if I had any faith in the chronology. But the more I learn of it, the less credibility it has.