Mythology is not a monolith. We're talking 3000+ years of cultural evolution across multiple cities that united and separated multiple times, each having their own local cult that rose to prominence or got supplanted by a different one.

When some of them got together and overlapped, they might have taken different facets of "death": Osiris is not strictly a god of death itself but a judge of your soul, and grants eternal life in death, while Anubis was a god of funerary rites and graves, so the physical aspect of handling dead bodies.

When a city took prevalence over another, either because the pharaoh set up shop there or because a temple in that city became more famous and gained influence, that city's major cult could overshadow other gods worshiped in other cities and take over their duties.

Then there were bigger gods that got cults that split into different aspects, like how Hathor and Sekhmet come from the same goddess but Sekhmet specialized in bloody war and the sun burning in the desert (an aspect she took from her father, a more general sun god) while Hathor specialized in motherhood.

Other aspects are passed around in the same way, starting with the role of sun, there are countless aspects of the sun that were embodied in different gods. Even the scarab is an aspect of the sun - because it emerges fully matured from the dungball of its parent the same way the sun comes out from the underworld in the morning, so there was a god for that. Death is a major aspect that remained a big constant in Egyptian religion, that's why those two are seen the most often.

If you look at which city becomes the center of Egypt's rule as time goes on through the different kingdoms and intermediate periods, and check which major temple is in that city, you see which cult takes over more duties.