Why do people have different chances of becoming Christian?

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 unrighteousness; 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 creeping things.

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 the law; 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 unto themselves: 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.

It doesn't matter whether some have a greater chance than others, as long as the chance for everyone is sufficient.

For since the creation of the world, God's invisible qualities -- His eternal power and divine nature -- have been clearly seen, being understood through what has been made, so that men are without excuse.

Romans 1:20

It is true that none are without excuse and it is true that before the foundations of the world God chose who would inherit salvation, but he locked up much of his methods in managing the universe to his planned ends under a mystery.

With many subjects, especially those that involve God's all powerful, all knowing and all wise management of the universe, we must start by acknowledging that we would not be able to comprehend how God will absolutely ensure all are judged righteously, and why he seems to give every opportunity to some and none to others, even if God explained it to us. We only know that he is just, loving and his ways perfect and past finding out.

However, starting from the standpoint of 'trust' we can believe that he loves the world and he can save any he chooses, just as easily for those with seemingly no chance as those with many opportunity. The world has a gradient of gospel light shining in it, some are raised up in homes in godly families where the gospel shines every day and some have as little light as many living three thousand years before Christ in a tribe far from Gods people. Yet it does not matter. As God is infinite he can reach anyone at any point in history, anywhere in the world equally. It only seems like some have more opportunity than others. God's infinite power in reaching the lost with the weakest means equals the playing field.

The only thing we know for certain is that he has chosen to save people only one way, faith in Christ alone. He also has chosen to reach the elect by delegating some of the outreach to his church. Of course where they might failI, he is strong enough to pick up the slack.

It seems hard to imagine how someone who has never heard of Jesus could have faith in him. But with God everything is possible and he is closer to us than our own breath. The Spirit is referred to as a wind as it blows into the lungs of every creature. The gospel actually cries out on every corner, of every street. Yet wicked men are so blind that they pay no attention even when it is put before their eyes. We we all at one time wicked in this way, but God plucked us out of the fire by his mighty hand.

The Reformed take on the answer is that no one becomes a believer by chance, but rather by divine election whereby God utilizes someone to preach the gospel to sinners, and causes the sinner to be regenerated (born-again), such that they receive the gospel as good news and believe in Jesus, and thus receive forgiveness of sins on account of Jesus' death on the cross and resurrection.