Here's why:
* Decomposition is a natural process: It's caused by microorganisms breaking down organic matter, and hair dye doesn't affect these microorganisms or their activity.
* Hair dye is a surface treatment: It primarily affects the hair shaft, not the underlying tissues or the body as a whole.
* Hair dye ingredients are not preservatives: While some hair dye components might have a minor antimicrobial effect, they're not strong enough to prevent decomposition.
In short, hair dye is meant to change hair color, not preserve a body. Decomposition will still occur naturally after death, regardless of whether someone had dyed their hair.