Probably because it's so boring. Being dead means that you can't hear what is being said or respond in any way, so talking to the dead is a massive waste of time. I don't know if the Bible prohibits talking to the dead, but it does explain this fact in Ecclesiastes 9:5 ("the dead know nothing") and some of the laws in Deuteronomy (you know, the ones that include not wearing clothes made from mixed cloths and not eating shrimp and stuff) say that this kind of time-wasting is abominable to God. So don't waste your time; talk to people who are still alive and can actually reciprocate instead!
Parenthetically, your avatar represents my favorite album by my favorite band. Good choice!
Ecclesiastes 9 King James Version (KJV)
9 For all this I considered in my heart even to declare all this, that the righteous, and the wise, and their works, are in the hand of God: no man knoweth either love or hatred by all that is before them.
2 All things come alike to all: there is one event to the righteous, and to the wicked; to the good and to the clean, and to the unclean; to him that sacrificeth, and to him that sacrificeth not: as is the good, so is the sinner; and he that sweareth, as he that feareth an oath.
3 This is an evil among all things that are done under the sun, that there is one event unto all: yea, also the heart of the sons of men is full of evil, and madness is in their heart while they live, and after that they go to the dead.
4 For to him that is joined to all the living there is hope: for a living dog is better than a dead lion.
5 For the living know that they shall die: but the dead know not any thing, neither have they any more a reward; for the memory of them is forgotten.
6 Also their love, and their hatred, and their envy, is now perished;
neither have they any more a portion for ever in any thing that is done under the sun.
7 Go thy way, eat thy bread with joy, and drink thy wine with a merry heart; for God now accepteth thy works.
8 Let thy garments be always white; and let thy head lack no ointment.
9 Live joyfully with the wife whom thou lovest all the days of the life of thy vanity, which he hath given thee under the sun, all the days of thy vanity: for that is thy portion in this life, and in thy labour which thou takest under the sun.
10 Whatsoever thy hand findeth to do, do it with thy might; for there is no work, nor device, nor knowledge, nor wisdom, in the grave, whither thou goest.
11 I returned, and saw under the sun, that the race is not to the swift, nor the battle to the strong, neither yet bread to the wise, nor yet riches to men of understanding, nor yet favour to men of skill; but time and chance happeneth to them all.
12 For man also knoweth not his time: as the fishes that are taken in an evil net, and as the birds that are caught in the snare; so are the sons of men snared in an evil time, when it falleth suddenly upon them.
13 This wisdom have I seen also under the sun, and it seemed great unto me:
14 There was a little city, and few men within it; and there came a great king against it, and besieged it, and built great bulwarks against it:
15 Now there was found in it a poor wise man, and he by his wisdom delivered the city; yet no man remembered that same poor man.
16 Then said I, Wisdom is better than strength: nevertheless the poor man's wisdom is despised, and his words are not heard.
17 The words of wise men are heard in quiet more than the cry of him that ruleth among fools.
18 Wisdom is better than weapons of war: but one sinner destroyeth much good.
I think from the context, they do not have any further knowledge what is happening "under the sun". It is possible for them to learn about things happening on this side of life by talking with someone who recently died and by angels who make side trips in heaven.
They do have memories of their life on earth.
Revelation 6:9-11 Easy-to-Read Version (ERV)
9 The Lamb opened the fifth seal. Then I saw some souls under the altar. They were the souls of those who had been killed because they were faithful to God’s message and to the truth they had received. 10 These souls shouted in a loud voice, “Holy and true Lord, how long until you judge the people of the earth and punish them for killing us?” 11 Then each one of them was given a white robe. They were told to wait a short time longer. There were still some of their brothers and sisters in the service of Christ who must be killed as they were. These souls were told to wait until all the killing was finished.
Also,
Isaiah 14 Easy-to-Read Version (ERV)
Israel Will Return Home
14 The Lord will again show his love to Jacob. He will again choose the people of Israel. He will give them their land. Then the non-Israelites[a] will join the Israelites, and both will become one family—Jacob’s family. 2 Those nations will bring the Israelites back to their land. The men and women from the other nations will become slaves to Israel. In the past, those people forced the Israelites to become their slaves. But in the future the Israelites will defeat those nations, and Israel will then rule over them in the Lord’s land. 3 In the past, you were slaves. People forced you to work hard. But the Lord will take away the hard work you were forced to do.
A Song About the King of Babylon
4 At that time you will begin to sing this song about the king of Babylon:
The king was cruel when he ruled us,
but now his rule is finished.
5 The Lord breaks the scepter of evil rulers;
he takes away their power.
6 In anger, the king of Babylon beat the people.
He never stopped beating them.
He was an evil ruler who ruled in anger.
He never stopped hurting people.
7 But now, the whole country rests and is quiet.
Now the people begin to celebrate.
8 You were an evil king,
and now you are finished.
Even the pine trees are happy.
The cedar trees of Lebanon rejoice.
They say, “The king chopped us down,
but now the king has fallen,
and he will never stand again.”
9 The place of death is excited
that you are coming.
Sheol is waking the spirits
of all the leaders of the earth for you.
Sheol is making the kings stand up
from their thrones to meet you.
10 They will make fun of you, saying,
“Now you are as dead as we are.
Now you are just like us.”
11 Your pride has been sent down to Sheol.
The music from your harps announces the coming of your proud spirit.
Maggots will be the bed you lie on,
and other worms will cover your body like a blanket.
12 You were like the morning star,
but you have fallen from the sky.
In the past, all the nations on earth bowed down before you,
but now you have been cut down.
13 You always told yourself,
“I will go to the skies above.
I will put my throne above God’s stars.
I will sit on Zaphon, the holy mountain where the gods meet.
14 I will go up to the altar above the tops of the clouds.
I will be like God Most High.”
15 But that did not happen.
You were brought down to the deep pit—Sheol, the place of death.
16 People will come to look at your dead body.
They will think about you and say,
“Is this the same man
who caused great fear in all the kingdoms on earth,
17 who destroyed cities
and turned the land into a desert,
who captured people in war
and would not let them go home?”
18 The kings of other nations lie buried with honor,
each king with his own grave.
19 But you were thrown out of your grave
like a branch cut from a tree and thrown away.
You are like a dead man who fell in battle,
trampled under the feet of other soldiers.
Now you look like any other dead man
wrapped in burial clothes.
20 Other kings have their own graves,
but you will not join them,
because you ruined your own country
and killed your own people.
So your wicked descendants will be stopped.
21 Prepare to kill his children,
because their father is guilty.
His children will never take control of the land.
They will never fill the world with their cities.
22 The Lord All-Powerful said, “I will stand and fight against those people. I will destroy the famous city, Babylon. I will destroy all the people there. I will destroy their children, their grandchildren, and their great-grandchildren.” The Lord himself said this.
23 “I will change Babylon. It will be a place for animals,[c] not people. It will be a swamp. I will use the ‘broom of destruction’ to sweep Babylon away.” The Lord All-Powerful said this.
