That the Pyramids were built as tombs for Pharaohs is totally devoid of supporting facts. No definitive proof has ever been found. Nonetheless, the myth continues without any shred of evidence to back it up. For talking purposes let us say that the Pyramids were built in pre-dynastic times. In our world today, the build up of infrastructure which began in the Middle East with the Greek city-states, which continued through the Roman era, which was expanded in Europe, and continued throughout the planet, is still going on.
Buildings keep getting bigger, bridges keep getting longer, dams keep getting larger.
The approaching millennium represents 2000 years of unbroken expansion. There is no remnant, or evidence of any build-up preceding their appearance. There is absolutely no archeological evidence of the evolution from caves, to huts, to bricks and mortar, to stone. No remains of any kind of tools with which advanced structure is possible. Without knowing how the Pyramids were constructed, it is impossible to know who built them, and just as importantly why they were built.