humans are what, 70% H2O ? bones less, soft tissue more. Coal on the other hand is little or none. now if you buried all that tissue in the ground for tens of thousands of years it may become combustible carbon based fuel. These tissues are just along for the ride as opposed to strictly being incinerated.then neither does:
"Burning carbon-based materials in order to create energy conversion has only been going on for the past 3500 years or so (Hint: think about steam-driven electric generation)."