What did they do wrong to deserve to go to hell?
I suppose one could ask what have they done to deserve to dwell with God in heaven? In its most fundamental sense, hell is complete separation from God. The utter separation from Him that hell imposes upon people, however, begins, to a lesser degree, before any of them sets foot there. In spite of what can be seen of God in what He has made, the Sentenilese, and many other people in areas of the world where the gospel is known, refuse to acknowledge their Maker. In spite of the many evidences of God's existence and the revelation of His character that these evidences provide, in spite of a deep, quiet, almost unconscious, awareness that God is, these people persist in living as separate from God as possible. They will have nothing to do with Him, but instead turn to worship of what He has made, or to worship of themselves. Thus, those who find themselves in hell merely find themselves in the final stage of a process of separation from their Maker that they began before they died. They are simply receiving in death what they chose in life.
In another equally fundamental sense, hell is punishment. It is intended to mete out the wrath of a perfectly holy God upon unrepentant sinners. No human, except Christ, has lived a perfectly righteous life. All of us contravene the dictates of our God-given conscience to serve ourselves in some way. We tell lies to avoid embarrassment or to hide our selfishness, we indulge to excess, we are cruel, or uncaring, or lazy, or cowardly, or too eager to be thought well of, or vain. We seek power, and pleasure and will often step on the next guy to get it. And we do all these things knowing on some level that we ought not to do them. Our conscience - if it is not too often violated - pricks us with guilt and shame when we act in contradiction to our God-given sense of right and wrong. Nonetheless, all of us have ignored our conscience, all of us have sinned. As the Bible declares,
"There is none righteous, no, not one." (Ro. 3:10) Consequently, our Holy Maker, if He is to be truly holy, must judge our sin. And in God's perfect judgment, our sin, which is always ultimately against Him, is so vile, so wretched, and so great that only an eternity in hell is an appropriate punishment for it.
Selah.