Why were pharaohs given such elaborate tombs?

The tombs evidence elaborate preparations for the next world, in which humans were promised continuing life and pharaohs were expected to become one with the gods. Mummification was used to preserve the body so that the deceased's eternal soul would be able to reanimate it in the afterlife.

Explanation:

Pharaohs were given such elaborate tombs because a) they were seen as physical manifestations of the gods and b) Egyptians believed that what was in your tomb was what you had in the afterlife.