It is true that Jesus died for the sins of the world but do you think that everyone has received forgiveness of their sins even if they do not accept Jesus?
This is how I understand it, taking it from the Gospel of John with the difference being between "sins" and "sin".
John 16:
8 And when he is come, he will reprove the world of sin, and of righteousness, and of judgment:
9 Of sin, because they believe not on me;
10 Of righteousness, because I go to my Father, and ye see me no more;
11 Of judgment, because the prince of this world is judged.
On the Cross Jesus paid for all sin and offers the gift of communion with God. The three things the Holy Spirit is working on are listed:
1) Of sin. Not the sins that have already been paid for bu(t for the "sin, because they believe not on me".
2) Of righteousness. It is finished. Right-standing with God has been satisfied.
3) Of judgment. Notice that it didn't say "mankind is judged" but simply the prince of this world is judged as hell was created for Satan.
As I view it, it goes as follow. Man is forgiven but, because of free will, he still has the option of rejecting the gift by not believing of Jesus who is the author and finisher of it. When one opts not to, he remains in association with the one that is judged, Satan. Guilty by association - not because man is judged but because Satan is judged and by rejecting Jesus (sin) - one enters into Satan's judgment.
Like you are driving a car, the man next to you gets out, robs the bank and kills the teller. You still get a murder charge even if you are driving.
Does that make sense?