The Great Commission is to spread the gospel for everyone to hear. What about the people that don't hear? Scripture tells us that they are without excuse.
because what may be known of God is manifest in them for God has shown it to them. For since the creation of the world His invisible attributes are clearly seen, being understood by the things that are made, even His eternal power and Godhead, so that they are without excuse. Romans 1:19-20
God's attributes are so clear through creation that there is no defense in rejecting it. Paul even gives an example of Gentiles.
for when Gentiles, who do not have the law, by nature do the things in the law, these, although not having the law, are a law to themselves, who show the work of the law written in their hearts, their conscience also bearing witness, and between themselves their thought accusing or else excusing them. Romans 2:14-15
I have heard the argument that God will save those who have not heard. However, if this were the case why would we spread the gospel. Wouldn't it be better to keep it a secret?
The heavens declare the glory of God; And the firmament shows His handiwork. Day unto day utters speech, And night unto night reveals knowledge. There is no speech nor language Where their voice is not heard. Their line has gone out through all the earth, And their words to the end of the world. In them He has set a tabernacle for the sun, Which is like a bridegroom coming out of his chamber, And rejoices like a strong man to run its race. Its rising is from one end of heaven, And its circuit to the other end; And there is nothing hidden from its heat. Psalm 19:1-6