It's because they think jesus will come and save them before they destroy the earth... or they think if the earth is destroyed then Jesus will come.
Look the earth is a six thousand year old experiment, due to come to an end any day now, at which point Gawd will wish away all the "good people" to the land of infinite rice pudding and Pureflix movies and let the left overs fight to the death for his amusement.
So why worry?
Be happy
Doo doo,da doo da da dooo (don't worry be happy)
Because God will lovingly cleanse it with fire and burn the non believers along with it. Then those who are pure of spirit in God's eye's (non Christian's need not apply) will return to their corpses and walk the Earth for all eternity.