In psychiatrists Rosman and Resnick's 1989 review of the necrophiliac literature, they found the motivation in 68% of the cases was a desire to possess an unresisting and unrejecting partner. This would appear to stem from feelings of powerlessness and rage, in turn originating in childhood neglect and sexual abuse.
However, in the discerning initiate, necrophilia may be the desire to be possessed by the 'unresistance' of Death itself, and it remains chief among the blasphemies encumbent upon the thoughtful Hessian to traverse. For such an initiate, the corpse is not a site on which he projects latent pain, but rather: their intercourse becomes the nexus of the Freudian death drive and the corpse's vivid display of Thanatos, expressing the initiate's twin drives of Eros's passionate thrust towards propagation/survival and the Thanatoic fearful/fearsome obsession with Death.
In that bewildering, apocalyptic twinning, we may find a blazing reorganisation of our very experience of Life.
How's that strike ya?