They started out as tombs, but, as grave robbers kept breaking in, it became cheaper to use the Valley of the Kings, which was easier to secure.
It came down to how much cash would be spent on protecting the Pharaoh’s treasures.
They started out as tombs,
—
Except no one broke into the Great Pyramid until the muslims tunneled into it around 700 AD - it was empty then.
The very early pharaohs like Khufu could well be buried under their funeral temples - there are mysterious ‘drains’ - the term Egyptologists gave them, that can’t actually drain anything as they slant upward and outward. There construction is such that they seem to be designed to hold or lower heavy weights. They have been neglected since their discovery in the early 20th and late 19th centuries. Egypt antiquities has allowed no further examination since other that a brief walkthrough by Robert Temple 20 years ago.
Pretty much everything coming out of modern Egyptology is in upheaval so what was ‘true’ yesterday is disputed today. Most dating is based on various Kings Lists and Manetheo’s List - even-thought some of this is known to be forgeries, Egyptologists still use them.
What’s important to remember is what every is told must fit the established theme - anything that endangers this is a threat to Egypt’s National Security as the lion’s share of the country’s income is from tourism. Doubts cast could make people believe the whole thing is a fake - like some believe the Russo-Ukraine war is - and the country would face another disaster.