Although the papyri in question date to the 20th Dynasty, they refer to a 17th Dynasty king. Let's see what the Egyptians said about pyramids and tombs, in their own words...
Quote
(We) found the burial-place of the royal wife Nubkhaas
his royal wife in the place. . . its (2) side.3 It was protected and . . . .ed
with plaster and covered with. . .4 We forced it open 5 also and we found her
(3) lying there likewise. We opened their outer coffins and their inner
coffins in which they lay. We found this (4) noble mummy of this king
equipped like a warrior (?).6 A large number of sacred-eye amulets and
ornaments of gold was at his neck, (5) and his headpiece7 of gold was on
him. The noble mummy of this king was all covered with gold, and his
inner coffins (6) were bedizenedg with gold and silver inside and outside
with inlays9 of all kinds of precious stones. We appropriated10 the gold
(7) which we found on this noble mummy of this god and on" his eye
amulets and his ornaments which were at his neck and on the inner coffins
in which he lay. (8) (We) found the royal wife just (?) likewise 12
and we appropriated all that we found on her too. We set fire to their
inner (g) coffins. We stole their outfit which we found with them, consisting
of objects of gold, silver, and bronze, and divided (10) them up
among ourselves. We made this gold which we found on these two gods
and on their mummies, their eye amulets and ornaments and their inner
coffins into eight (parts).
THE GREAT TOMB ROBBERIES OF THE TWENTIETH EGYPTIAN DYNASTY, T. ERIC PEET, p. 48
Confessions of a tomb robber. Right down to the burning of the bodies, which is evidenced in the remaining mummy parts we have from Sneferu's pyramid in the Fourth Dynasty.
They seemed perfectly comfortable with pyramids being the tombs of kings. Who are we to question them without any evidence to the contrary?
Anthony
You can lead a horse to water but you can't make him think.