In their lifetimes - for should they touch a corpse, adumbrate over it, or similar, the impurity of the corpse sticks to them and does not wish to depart without the great effort which the Torah prescribes: the mitzvah of the red cow. In their deaths - the impurity also is great…
I have already explained this in a parable. It is compared to two vessels owned by a householder - one full of honey and one full of waste. He empties them and removes them from the room. The one which contained the honey attracts a swarm of flies and insects; the one which contained the waste, although it attracts a few insects, it is not comparable to the honey. So too, when a Jew dies, since he was filled with sweet and beautiful holiness, when the soul departs and the body is emptied out, the unholy husks, which are the forces of impurity, gather without end. They always wish to stick to something holy to enjoy its sweetness.
(Ohr HaChaim to BeMidbar 19:2)