I can think of only two reasons for it. To make a statement of the destructiveness of war (various war memorial cemetaries), and to give archaologists and anthropologists something to dig up 100 to 1000 years later to see how we lived.
Other than that, why bother. The notion of your physical body needing to be preserved has long past.
It takes up useful space. Its very expensive. Your organic remains, which can be placed back into the cycle of life gets locked up in a coffin. After a few years your relatives will also die and you will be forgotten.
There are better things to do with a dead corpse than bury it. Donate it to science or burn it into ash, I say.