Man has a free will..he may do what he wills at all times..the question at hand is why do some will to follow Christ and some not??
Do you believe in original sin?
I guess I don't see what is so difficult to understand about this. If man has free will, then man can freely choose to follow God or not to follow God. Why would a man choose NOT to follow God? As many reasons as there are men, probably. It is not always easy to do the right thing. It conflicts with our other desires. It doesn't always give us immediate gratification.
Do you believe in original sin?
For those playing along at home, I should probably point out that I do not believe in original sin, nor do I believe in an eternal hell. I'm about as un-Calvinist as you could get! :o)