For the same reason people rob banks, jewellery shops, and so on - greed. You would also have corrupt priests who would divulge the location of graves for a fee or pay-off.
Human nature has not changed since the time of the pharoahs!
they usually were very sneaky when they robbed the graves. sometimes, robbers were guards, so while on duty, they would sneak in and steal the goods
So they could steal all the valuables left with the dead, which was supposed to aid the dead in the afterlife.
Money
Tomb robbers.
Some tombs were empty because grave robbers robbed the tomb of its riches.
Pharaohs hid their tombs because they were afraid of robbers robbing the tombs so they tried to hide them away from robbers.
The pharaohs' tombs were primarily emptied by raiders. However, there were some tombs whose mummies were able to be saved. One of the most famous pharaohs to have been rescued was King Tut.
They built false entrances and doors, along with traps, to protect the tombs of pharaohs from tomb-robbers; without these traps and false entrances, tomb-robbers would take the valuable artifacts that the pharaohs were buried with.
Since many of the tomb robbers were the workers they began to rob the tombs almost as soon as they were finished and the funeral items were put into them.
Tomb robbers.
Some tombs were empty because grave robbers robbed the tomb of its riches.
Pharaohs hid their tombs because they were afraid of robbers robbing the tombs so they tried to hide them away from robbers.
The tomb of Tutankhamun in the Valley of the Kings is notable for being one of the few royal tombs in Egypt that was discovered mostly intact by archaeologists in the 20th century, escaping the fate of being looted by tomb robbers.
Egyptian tombs were move to foil the effort of grave robbers who raided them for the treasures with the dead.
mummies normally stayed in their tombs . the only time a mummy would leave it's tomb is when it was stolen by tomb robbers or was legally taken by museums with permission from the "mayor" of the town .
they got into the museum because the doors were not locked and they opened the door. Stole the tombs
Your right, they would steal all kinds of treasures
At first they built those big tombs to show off their power and wealth, but soon they realized that the bigger and richer looking the pyramid was, the more likely to be a target for tomb robbers. So they stopped building pyramids and started digging tombs in the Valley. Unfortunately, tomb robbers still managed to find them. The only known tomb to be completely untouched, with nothing stolen, is the tomb of King Tut.
Tombs were made to protect the pharaohs form either great robbers, floods, and animals. Tombs are made to house the dead. Because a tomb is costly, it is usually used to house the bodies of nobility or the very wealthy.
The pharaohs' tombs were primarily emptied by raiders. However, there were some tombs whose mummies were able to be saved. One of the most famous pharaohs to have been rescued was King Tut.