This question has been asked since the Gospel has been revealed, and Christians have come up with many possible answers. There's a list of them here: http://rsc.byu.edu/archived/salvation-christ-comparative-christian-views/13-those-who-have-never-heard-survey-major-pos
Your question is very similar to a question asked previously on this site: What about all those who just don't know? but yours is slightly different. Instead of asking what happens to those people, you seem to be asking "Why would God allow this?"
To set where I'm going with this:
- The answer to "What happens to them" isn't agreed upon by everyone. Some believe that they will be able to be saved based on obedience to their conscience, or via some other mechanism. For the point of your question, however, those opinions don't matter because if they are saved, we don't have to ask why God would allow it. So I assume, from the context of your question that you're in the "They will not be saved"camp.
- The next question that follows in this line of thinking is "How can a just God allow this?" Often this comes from those who are trying to prove that the Christian God is not just. However, several answers have been given to that question.
One of those answers is among the classic apologetic answers, that addresses your question specifically.
Romans 1 touches on the subject of whether or not we are held guilty if we've never heard the Gospel message. It lays out a few truths:
- God reveals Himself to us, and we are without excuse.
- Our ancestors had access to the truth of God, and chose to turn from them.
Romans 1:18. (KJV) For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hold the truth in
19. Because that which may be known of God is manifest in them; for God hath shewed it unto them.
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.
22. Professing themselves to be wise, they became fools,
23. And changed the glory of the uncorruptible God into an image made like to corruptible man, and to birds, and fourfooted beasts, and
Their unbelief and rebellion against God meant that their children, their children's children, and so on were not taught about God. It's not His fault, it's theirs. Because they chose to rebel when they knew the truth, and didn't teach their children, they doomed their children to not knowing the truth of God. This is one reason that Proverbs 22:6 is important. (Again, KJV)
Train up a child in the way he should go: and when he is old, he will
not depart from it.
In Romans 2 (KJV), we read:
11. For there is no respect of persons with God.
12. For as many as have sinned without law shall also perish without law: and as many as have sinned in the law shall be judged by
13. (For not the hearers of the law are just before God, but the doers of the law shall be justified.
14. For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law
15. Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while
accusing or else excusing one another;)
These peole fall into this category, not knowing about the Hebrew God, or Jesus as one who "sinned without the Law", and Scripture here tells us that "he shall perish without law". To those that believe they will perish, they will perish because he has sinned, and ignored the conscience that God has placed in each and every one of us.
So in summary, the reason that some people live in areas where it's harder to hear the Gospel, it's because the people in those areas, or their ancestors chose to reject the Gospel and make it hard to have access to it.