The Graffito of Esmet-Akhom in the temple of Philae is the last known use of hieroglyphs in ancient Egypt, but why did they stop being used?

A joint French-Egyptian team found the carvings underwater south of Aswan ... Aswan is also home to the Philae temple complex ...

such as the Great Temple at Abu Simbel, carved out of an escarpment of solid rock. Its design and layout allow rays of the sun to penetrate to the innermost chamber twice annually on the equinoxes.