What is the wisdom behind the preservation of the pharaohs' bodies, mummified until now, and why have their bodies not decayed despite the passage of thousands of years?

The pharaohs' ability to mummify the dead does not validate their beliefs. Allah granted them worldly knowledge and honor on Earth, just like previous nations whom Allah destroyed due to their tyranny, despite their strength and knowledge. These blessings did not prevent Allah's punishment from reaching them; rather, He destroyed them to serve as a lesson.