They dont believe because Christ didnt die for them as He did His Sheep Jn 10:26
26 But ye believe not, because ye are not of my sheep, as I said unto you.
Believing in Christ comes with the fact He died for you. So if one never believes, its because He never died for them taking away their sins. See His Death takes away sin and its awful consequences 1 Jn 3:5
And ye know that he was manifested to take away our sins; and in him is no sin. Unbelief is the consequences of sin
Nowhere in the Bible says Jesus did not die for them.
You are creating this definition by
your own reasoning which is a form of idolatry.
From a once great Calvinist who left the Cult:
“GOD SOVEREIGNLY DECREED THAT MAN SHOULD BE FREE TO EXERCISE MORAL CHOICE, AND MAN FROM THE BEGINNING HAS FULFILLED THAT DECREE BY MAKING HIS CHOICE BETWEEN GOOD AND EVIL. WHEN HE CHOOSES TO DO EVIL, HE DOES NOT THEREBY COUNTERVAIL THE SOVEREIGN WILL OF GOD BUT FULFILLS IT, INASMUCH AS THE ETERNAL DECREE DECIDED NOT WHICH CHOICE THE MAN SHOULD MAKE BUT THAT HE SHOULD BE FREE TO MAKE IT. IF IN HIS ABSOLUTE FREEDOM GOD HAS WILLED TO GIVE MAN LIMITED FREEDOM, WHO IS THERE TO STAY HIS HAND OR SAY, ‘WHAT DOEST THOU?’ MAN’S WILL IS FREE BECAUSE GOD IS SOVEREIGN. A GOD LESS THAN SOVEREIGN COULD NOT BESTOW MORAL FREEDOM UPON HIS CREATURES. HE WOULD BE AFRAID TO DO SO.” –
A.W. TOZER, THE KNOWLEDGE OF THE HOLY: THE ATTRIBUTES OF GOD