What picture comes to mind when you think of Hell?
That's why. The thought of everlasting suffering in fire for eternity. Suffering forever due to finite transgressions tends to be a very unpalatable image. Those "fire and brimstone" preachers of ages past screaming about death and suffering in tent revivals , for example.
How many people filed to the front of the tent for salvation because they didn't want to burn?
There is an atheist on YouTube who burned in an accident. And he accounts his near death experience as one where he went to Hell. He's now a convert to Christ.
When Emmanuel was speaking of Gehenna, it was the place of constant fires outside the city of Jerusalem. There the locals refuse was burned, as well as the bodies of the condemned crucified, or killed in some other capital punishment method and who's family could not afford a tomb or burial. The dead were consumed in the fire. And according to Jewish law, those who perished died in their sin.
Powerful parable that our precious Emmanuel delivered concerning what was a grave for those who would not be interred any other way. And for those who were not Jewish , a powerful image lesson concerning the scrolls and obedience to God's laws so as to not die outside of the faith and in sin.
I personally can't imagine the sight or the smell or how the sky would look with that constant smoke and embers filling the air. Lord have mercy.
Matthew 10:28
And do not fear those who kill the body but cannot kill the soul. Rather fear him who can destroy both soul and body in hell.
Romans 6:23
For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord.