Why did they anoint dead bodies with herbs and spices after burial?

It was the custom to anoint the body of the deceased with herbs and spices even a day or so after burial. They were not buried underground but placed in a cave, as noted in the account of resurrection morning in John chapter 20.

Les explains that it was the custom to anoint the body of the deceased with herbs and spices even a day or so after burial. He points out that they were not buried underground as we think of it, but placed in a cave. This custom is mentioned in John's Gospel chapter 20 on resurrection morning, when Mary Magdalene came to the sepulcher early while it was yet dark and saw the stone taken away. Peter and John then ran to the sepulcher, with Peter entering first.

When did Jewish people anoint a body with spices after burial?

As the custom was, Jewish people anointed the body of the deceased with herbs and spices even a day or so after burial. They were placed in a cave, not buried underground. So Mary Magdalene came to the sepulcher on the first day of the week early, before daylight, while it was still dark.