Because traditional Christianity has twisted the concept of hell. In the original languages, the bible speaks of no such place for humans. The hell, so commonly thought of today, is reserved for satan and his demons.
Biblically, the words translated as or associated with "hell" are "sheol"/"hades" -which refer to the grave, "tartaros" -which is the place or state of restraint of the sinning angels, and "gehenna" -which is actually the name of a place outside Jerusalem where trash was continually burned, but refers to the lake of fire into which the beast and false prophet are cast first -Satan also about a thousand years later -and men whose works make them deserving of such in God's view.
Luk 12:5But I will forewarn you whom ye shall fear: Fear him, which after he hath killed hath power to cast into hell; yea, I say unto you, Fear him. (Hell here =gehenna [not hades -which is also translated "hell"])
HOWEVER... There are many verses which suggest that, though the fire is never quenched, at least not all who are cast into it remain there literally "forever" -as in with no possibility of being removed from it to life or death.
Mar 9:47 And if thine eye offend thee, pluck it out: it is better for thee to enter into the kingdom of God with one eye, than having two eyes to be cast into hell fire:
Mar 9:48 Where their worm dieth not, and the fire is not quenched.
Mar 9:49 For every one shall be salted with fire, and every sacrifice shall be salted with salt.
Mar 9:50 Salt is good: but if the salt have lost his saltness, wherewith will ye season it? Have salt in yourselves, and have peace one with another.
The above suggests that even the gehenna lake of fire might work good. It says their worm dieth not (they do not decay) and the fire is not quenched -that everyone is salted with fire (though not all by the gehenna fire) -and that salt is good. Those who repent before the judgment have no need to be cast there (no human beside the beast and false prophet will be cast into gehenna until the judgment -which is after the millenium) -and being cast into the lake of fire might be the point at which some finally do repent. Here are some verses suggesting so...
1Co 3:13 Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is.
1Co 3:14 If any man's work abide which he hath built thereupon, he shall receive a reward.
1Co 3:15 If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
"The fire" is not necessarily the gehenna fire -though it includes gehenna, but is God's judgment generally -as it says...
Mal 3:2 But who may abide the day of his coming? and who shall stand when he appeareth? for he is like a refiner's fire, and like fullers' soap:
Mal 3:3 And he shall sit as a refiner and purifier of silver: and he shall purify the sons of Levi, and purge them as gold and silver, that they may offer unto the LORD an offering in righteousness.
Zec 13:9 And I will bring the third part through the fire, and will refine them as silver is refined, and will try them as gold is tried: they shall call on my name, and I will hear them: I will say, It is my people: and they shall say, The LORD is my God.
Rev 3:18 I counsel thee to buy of me gold tried in the fire, that thou mayest be rich; and white raiment, that thou mayest be clothed, and that the shame of thy nakedness do not appear; and anoint thine eyes with eyesalve, that thou mayest see.
Rev 3:19 As many as I love, I rebuke and chasten: be zealous therefore, and repent.
...but gehenna is essentially an ultimatum. God will not allow evil into eternity -and anyone not willing to repent will be cast into the lake of fire.
There are only so many potential options -living forever, dying, being tormented forever... However, God gave us a choice between two things -
life and death -and this should be considered when understanding gehenna.
We can live forever if we choose to do right -or we can die. Gehenna will not be quenched, but we will
eventually die completely -be utterly destroyed -if we absolutely refuse to repent. Some believe the body can die, but the "soul"(actually "spirit") is immortal -but this is not the case. Both the body and spirit can be completely destroyed in gehenna -as it says...
Mat 10:28And fear not them which kill the body, but are not able to kill the soul: but rather fear him which is able to destroyboth soul and body in hell. (soul=G5590=psuche/spirit, hell=G1067=gehenna)
The following says that some will have their part in the lake of fire...
Rev 21:6 And he said unto me, It is done. I am Alpha and Omega, the beginning and the end. I will give unto him that is athirst of the fountain of the water of life freely.
Rev 21:7 He that overcometh shall inherit all things; and I will be his God, and he shall be my son.
Rev 21:8 But the fearful, and unbelieving, and the abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death.
In the above, "shall have their part in" might suggest that not all who are cast into gehenna remain there without end. The bible also says that death and the grave will also be cast into gehenna -and utterly destroyed. For those who absolutely refuse to repent, it will be their complete end. It will also be the end of death -the end of people going to the grave.
No one has been cast there yet.
Everything God does is to give every angel and man every chance to choose rightly. His will is that we all live forever, but we must choose. Perhaps, having not responded to anything else and faced with this ultimatum (and obvious proof of God's existence), etc... all men will repent. This certainly puts the following into perspective...
1Co 15:21 For since by man came death, by man came also the resurrection of the dead.
1Co 15:22 For as in Adam all die, even so in Christ shall all be made alive.
1Co 15:23 But every man in his own order: Christ the firstfruits; afterward they that are Christ's at his coming.
1Co 15:24 Then cometh the end, when he shall have delivered up the kingdom to God, even the Father; when he shall have put down all rule and all authority and power.
1Co 15:25 For he must reign, till he hath put all enemies under his feet.
1Co 15:26 The last enemy that shall be destroyed is death.
We must choose, and God will utterly destroy all who utterly refuse to do rightly -but perhaps God knows what it will take for each of us to choose rightly -and will bring it to pass.
The ultimatum of gehennna is quite necessary.
