Two things that are of foundational importance to understand here are that God has both inscribed His moral laws into our hearts (Romans 2:15) and manifested Himself plainly through nature (Romans 1:18-20). He is not far from any one of us (Acts 17:26-27). A person's invincible inability to attain knowledge of Jesus Christ for whatever reason is not the problem. The real issue is that our sins against Him have placed us under condemnation.
Even though Scripture acknowledges men such as Cornelius who had feared God prior to receiving the message of the gospel, the New Testament still records the Lord directing the man to the Apostle Peter so that he could receive the good news of salvation (Acts 10). In addition, God does take into account one's ability to understand His precepts in judgement (John 15:22; Romans 2:12-13). The people who knowingly and willingly rebel against God and reject His message of forgiveness are under condemnation. Every person who has a rational mind is culpable.
If every unbeliever is automatically saved just because of a lack of knowledge regarding the Person of Christ and His atonement, then the gospel that we preach would be needless. In fact, the concept of evangelism would be rendered nonsensical. We are saved by the grace of God through faith in His Son Jesus Christ. We should be making the greatest effort possible to ensure that everybody gets a chance to hear the gospel. That is the underlying goal of the Great Comission. We should be grateful that God has provided even one way for us to be reconciled with Him (John 14:6; Hebrews 4:14-16).