The Valley of Kings tunnel tombs are lousy with texts, sealed in. So it can't have been meant for visitors.
I am always mystified at how there could be never any soot on the ceilings. We look at these things all brightly lit up, but people writing them were in a very deep hole in the ground.
A simpler explanation for why the Pyramids of Giza were not usurped: By the time royals began routinely usurping earlier royal tombs (late New Kingdom/early Third Intermediate Period), the pyramids and mastabas of the Old Kingdom were long out of fashion as burial sites.
The Valley of Kings tombs were tunneled deep into living bedrock. How they did, I do not know, but ancient people worldwide seemed to have no difficulty cutting unlimited amounts of stone.