In some things, God's will is determinate (thelema), not to be superseded by adversaries. But in other things, He has a preference (boulomai), but will allow one's contrariness to prevail. Regarding one's eternal destination, Peter described it this way:
"The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance" (2 Pet. 3:9 AV; here "willing" = boulomai, not thelema).
That is, in this matter so as to leave the human a quality of individualism, and not be an automaton, The God greatly prefers that an individual be saved from perishing, but if the human's oppositional defiance reigns (and He allows it) despite all His counsel and warnings, the person may choose otherwise, whether deluded or just plain too proud to admit his depravity.
But God does know what the decision will be, though arguing against it in his patience and mercy. If any one rejects the Gospel as authored by Jesus, he will have refused The Father's offer to graciously impute Christ's righteousness to the sinner's account, and will thus be without excuse when God insists that the debt be paid (Rom. 1:20).
With an ache for those who thus choose, I also believe that nevertheless few--not many--will enter the heavenly kingdom of God (Mt. 7:13-14). But that's apparently what Jesus said, and I suppose it is true.
And ...
Joh 6:65 And he said, "This is why I told you that no one can come to me unless it is granted him by the Father."
In fact, the entire chapter of John 6 will make no sense at all. Belief must be granted by the Father. Nicodemus couldn't understand the concept...
People cannot understand the gospel unless it is willed by the Father.
Mat_13:13 This is why I speak to them in parables, because seeing they do not see, and hearing they do not hear, nor do they understand.
This was foretold by Isaiah.
But unless we understand this simple concept as our Lord told Nicodemus it is difficult for us to correctly teach the gospel.
If the numerous scriptures that plainly state this fact does not convince one, then there are numerous scriptural examples of God directly stepping into the conversion process such as Moses with the burning bush, Samuel call from the ark, Samson call before he was born, and Paul's conversion on the Damascus road to name but a few.
The problem isn't about why God would allow people to go to hell. We all deserve that destiny. The issue is really about why God would want to save any of us.