The so-called sarcophagus in the ‘Kings Chamber’ was placed before the Pyramid was finished as it is too large to fit in the existing passage pays. Further, when the pyramid was first opened in the 7th century to loot it - the ‘thieves entrance’ - nothing was found anywhere inside, there never was a lid. And the box is not gigantic but about 6 feet long and 3 wide and 4 feet high or so.
Lidded gigantic sarcophagi are found elsewhere by the dozen - thought to be burial sarcophagi of sacrificial bulls - but no bones or any other remains have ever been found. There are also similar sized sarcophagi in the Well of Osiris, but again empty.
The Great Pyramid was open to tourists during Roman times, and probably for some while before that. The Byzantines sealed it back up. After the muzzie invasion, it was only a matter of time before the caliph decided to try to crack it open and look for loot. They cut the robber's hole that used as the tourist entrance today, and probably the robber's hole that leads from the descending passage to the Grand Gallery.
It's not unlikely that the caliph's thugs entered the "Queen's chamber" (which probably had burial goods and/or the canopic jars) and the burial chamber, and removed the mummy at that time, and the lid was possiblly just smashed into fragments in the process -- then the fragments were removed by visitors as souvenirs.
See the photos and text here -- the granite block the caliph's thugs pushed into the chamber upon their entry, which used to set on the floor near the foot of the sarcophagus, is now missing, presumably removed by Egyptian authorities.
Ok, try this.
The pyramid interior is a temperature and pressure constant environment and the stone receptacle is the standard measure. The standard measure is used to certify volumes for trade in grain and other volumetric commodities needing a standard.
The pyramids at Giza have multi functions including indicating the solstice. indicating the true north south bearings, and permanent geodesic markers for surveys plus lots more.
The Giza pyramids are commercial in nature rather than religious