A person dies in unbelief because they were not one of Christs sheep that He died for Jn 10:26
Acts 14:2 - But the Jews who refused to believe stirred up the other Gentiles and poisoned their minds against the brothers.
Acts 19:9 - But some of them became obstinate; they refused to believe and publicly maligned the Way. So Paul left them. He took the disciples with him and had discussions daily in the lecture hall of Tyrannus.
While Calvinists will deny this, believing or refusing to believe the gospel is a choice that man is free to make.