Because the dead can't return to the land of the living, according to
Job and
Solomon, who both also say the dead
don't know anything or
perceive anything. Therefore "Samuel" was not Samuel, but an imposter, which is why the Lord did not want anyone engaging in Spiritualism.
Scripture clearly states it was Samuel not an imposter.
11 Then said the woman, Whom shall I bring up unto thee? And he said, Bring me up Samuel.
12 And when the woman
saw Samuel, she cried with a loud voice: and the woman spake to Saul, saying, Why hast thou deceived me? for thou art Saul.
13 And the king said unto her, Be not afraid: for what sawest thou? And the woman said unto Saul, I saw gods ascending out of the earth.
14 And he said unto her, What form is he of? And she said, An old man cometh up; and he is covered with a mantle.
And Saul perceived that it was Samuel, and he stooped with his face to the ground, and bowed himself.
15
And Samuel said to Saul, Why hast thou disquieted me,
to bring me up? And Saul answered, I am sore distressed; for the Philistines make war against me, and God is departed from me, and answereth me no more, neither by prophets, nor by dreams: therefore I have called thee, that thou mayest make known unto me what I shall do.
16
Then said Samuel, Wherefore then dost thou ask of me, seeing the Lord is departed from thee, and is become thine enemy?
17 And the Lord hath done to him, as he spake by me: for the Lord hath rent the kingdom out of thine hand, and given it to thy neighbour, even to David:
18 Because thou obeyedst not the voice of the Lord, nor executedst his fierce wrath upon Amalek, therefore hath the Lord done this thing unto thee this day.
19 Moreover the Lord will also deliver Israel with thee into the hand of the Philistines: and to morrow shalt thou and thy sons be with me: the Lord also shall deliver the host of Israel into the hand of the Philistines.
20 Then Saul fell straightway all along on the earth, and was sore afraid,
because of the words of Samuel: and there was no strength in him; for he had eaten no bread all the day, nor all the night.