Lack of evidence. How many people are there who wouldn't want to say no to eternal life, and therefore would turn to God if they knew for certain, but simply don't know for certain that God exists, and therefore don't become christians? I may be wrong of course, God knows the answer to that question better than me, but I'd have thought there were loads of people in that position.
I agree. I think most nonbelievers are looking for proof or evidence of God's existence (as if the indescribable beauty in nature, miracles, the Word and infinite Christian testimonies aren't enough).
I don't understand why a God of love and justice would punish people just for not knowing for certain and choosing not to believe. And if God really loves us that much, I don't understand why he doesn't want to let us KNOW that!
It is clear that God values faith. (2 Chronicles 20:20, Isaiah 7:9, Matthew 13:58, Mark 11:22, Mark 16:14, John 14:12, Acts 20:21, Romans 1:17, Romans 3:28 among many others)
Without faith, we are living in pride, relying solely on our intellectual ability to "understand" God. Faith allows us to put aside our humanly pride and look to the only One who has all the answers.
As for who God chooses to punish, who are we to ask? But I don't believe God wants to punish anyone. He wishes for all men to come to Him for salvation. When people purposely choose to deny faith, they set themselves apart from God.