Over 1000 years passed between the construction of the Great Pyramids and the time when the Valley of the Kings started to be in use. Of course decorative styles would be different!
It's not very surprising that we don't have a lot of texts about the construction of buildings that are 4,500 years old. The pyramids are incredibly ancient, and were ancient when later pharaohs tried to understand who built them.
For comparison, the Notre Dame of Paris is closer to our time than the Pyramids were to the pharaohs who built their tombs in the Valley of the Kings.
It's not very surprising that we don't have a lot of texts about the construction of buildings that are 4,500 years old. The pyramids are incredibly ancient, and were ancient when later pharaohs tried to understand who built them.
For comparison, the Notre Dame of Paris is closer to our time than the Pyramids were to the pharaohs who built their tombs in the Valley of the Kings.