Questions about burials

Why are graves dug so deep (it's distressing to see the coffin go down so deep)?

Graves have to be dug to a sufficient depth to allow for future burials to take place should a family require more than one burial in a grave. Therefore, the grave needs to be deep enough to allow not only for the depth of coffins/caskets that will be buried but also to accommodate legal requirements of undisturbed earth to be between each coffin and the amount of earth that must cover the last interment.