Correction: God never threatens anyone with hell, he just warns us against ending up there by choice.
People go to hell because they choose a path that leads away from God's gracious and abundant provision of eternal life with him in his heavenly habitation; i.e., they make choices that separate them from God's life-giving presence.
Unfortunately, the only alternative eternal habitation for the human soul is hell, which was prepared for the devil and his angels as judgment and punishment for their rebellion against God and his rule. Whoever rejects God and his ways therefore ends up there instead.
That's why Jesus came to earth to proclaim God's Kingdom, pay the price of our deliberate acts of rebellion against God and offer us the gift of eternal life. The Bible serves as a record of all this so that we can all read it and make our own informed choices.