Because they have chosen not to believe. Everyone has that choice.
20 For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse :
21 Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened.
KJV
Mark 16:15-16
15 And he said unto them, Go ye into all the world, and preach the gospel to every creature.
16 He that believeth and is baptized shall be saved; but he that believeth not shall be damned.
KJV
John 3:18
18 He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God.
KJV
God is capable of speaking to anyone. There are athiests on this board that hear the truth every day and they mock it and reject Him. They are the ones that are really in danger. A person in a remote location that has never heard of Christ is not in as much danger (in my opinion). God can speak to them and offer them His truth as the first verse I listed says.