You are quite mistaken. Believing is God's REQUIREMENT.
John 6:29 - Jesus answered, “The work of God is this: to believe in the one he has sent.”
The Jews' question: v.28 - Then they asked him, “What must we do to do the works God requires?”
1 Cor 1:21 - For since in the wisdom of God the world through its wisdom did not know him, God was pleased through the foolishness of what was preached to save those who believe.
John 6:29 - Jesus answered, “The work of God is this: to believe in the one he has sent.”
The Jews' question: v.28 - Then they asked him, “What must we do to do the works God requires?”
1 Cor 1:21 - For since in the wisdom of God the world through its wisdom did not know him, God was pleased through the foolishness of what was preached to save those who believe.
John 6:29, says that it is God's work that someone believes. So, the only work then that will satisfy God, and is that which He requires (v28), is His work alone. This means belief is God's work, not ours. So, since not everyone comes to a true belief, God then obviously doesn't give it to everyone.
For 1 Cor 1:21 - if it is the work of God for someone to believe (as you said above), then the belief of this verse must also be of the work of God, which belief He does not give to everyone.