This intriques me,because I often wondered myself.
There could be several reasons why a member of the family show themselves to us here on the physical plane.

They have recently passed over and wish to convey that they are still very much 'alive' in the spirit realms.

They wish to give a message to someone dear to them,again that this is proof that they still exist.

They also can appear in the dream state,again with same purpose in mind.

Deepsea