That's an entirely legitimate question. It would, however, do away with large elements of archaeology.

Burial practices vary with culture: there is no one right way. Even within the UK there has been a wide range of different approaches to the right way to treat a body.

I believe that death is the end of the person, and the body is just waste material. However, many others do not feel that way, so it is reasonable to wait until everyone who knew that person had also died, so that there was no longer a direct connection. This is to pay due respect to the living: the dead need no such. Let alone those who can only be identified as such by stains in the soil, and the trinkets they left behind.