Why did the ancient Egyptians build those pyramids?

There are many theories about the reasons for the building of the pyramids. These theories range from being tombs to astronomical observatories to paying homage to the gods.

The question that should be asked is why the Egyptians stopped building pyramids after the death of Khafre since these people had been building pyramids for a 1000 years before the ones at Giza.

Pyramids were built as tombs mainly during the Old and Middle Kingdoms (2700-1700BC) although Piye (about 721 BC) and Taharqa (about 664BC) lived considerably later. The Kings of Meroe also built pyramid tombs, influenced by the Egyptians, between 300BC and 300 AD.

Judging from the evidence and our current understanding of it, the most likely reason is that the pyramids mirrored the shape of the primordial mound from which creation began as well as the shape of sun beams so aided the King/Queen's rebirth as a God.

I know these days when you create something new that Noone else has come up with you try and show it off to the world. Why would it be diferent back then?