I am by no means a historian but take an interest in history.

It wasn't uncommon for palaces and pyramids to be scavenged for building projects. One example is Amenhotep IV, one of Egypt's most infamous pharaohs, who pushed the New Kingdom away from their traditional religious beliefs and established a monotheistic cult of Aten. His palace was more or less a bustling city. After his death, the city was abandoned rather quickly, but not without the inhabitants taking whatever items and treasures were in Amenhotep's city.

Pyramids were certainly scavenged as well. Many construction projects utilized stones from Old Kingdom pyramids. One difference, however, is the purpose of the pyramids/burial grounds. There were smaller temples built alongside or inside the pyramids or tombs of pharaohs so that surviving family members could make offerings to the deceased. These tombs that were being used didn't make good grave robbing targets, so we really don't see much tomb robbing until the Libyan and later dynasties when the cults of former pharaohs died off.

All my information comes from Toby Wilkinsons's The Rise and Fall of Ancient Egypt. I don't have the book with me here unfortunately, so I don't have the specific pages, but I hope this helps. If I have any errors I'll ask any professional historians to point them out.

I'm going to broaden the question a bit, out from just the Pyramids to the tombs in general:

The Egyptian belief system put a huge emphasis on the afterlife, but most of that belief centered on the tomb; there was no particular significance placed on the other material remains of the previous Pharaoh (i.e. their palaces).

There were entire bureaucracies devoted to the maintenance of the tombs. Including police forces.

The official cults of Egypt were fundamental to the structure of the entire society. Maintaining the tombs was, in some ways, no different than maintaining the government. Similar to how the splendor of medieval cathedrals was central to the power of the Catholic church.

The pyramids at Giza are made from some really big blocks. It took the entire state apparatus to build them and it would have taken a similar effort to dismantle them. Except for the original limestone sheathing. People might have stolen parts of that.

The pyramids have always been an identifying part of the city and the residents were/are proud of them. "Why haven't the Americans melted down the Statue of Liberty?" Because they like the Statue of Liberty.

Tombs, including the pyramids, were out in the "red land" (that is the desert) and no one really needed that land for anything other than tombs. Because the red lands are hot, dry and just terrible. Nothing will grow there. The palaces were in or adjacent to the "black land" (that is, the Nile's floodplain) and therefore occupied valuable real estate.

Many of the palaces did survive for quite a while, but they were often in cities and cities change over time. New ideologies took hold, new priorities. Meanwhile, the desert remained the desert forever and no one had any use for it.

Tombs are largely under ground. Once they are looted (which they almost universally were), tombs are effectively squared-off caves with some paintings on the walls. The pyramids don't even really have any paintings on the inside. They're pretty utilitarian.

Palaces were built of useful stone blocks.

Unless they weren't. Many palaces were probably built of mud brick, as was almost everything else. Mud brick is practical in Egypt, as there's very little rain, but only in the short term. Over the years, even Egyptian mud brick will melt.

Some Pharaohs built new palaces, others did not. It largely depended on how prosperous Egypt was at the time.