People believe what they want to believe,and when they have their mind set to not believe the Bible they will not believe it.
Jesus said if they do not listen to the words of God and do not want to believe,they will not believe even if one rose from the dead and told them.
When they have that mindset to not believe,and not believe in a God,the natural man does not understand the things of God,they have a reprobate mind,and the flesh will rebel against the word of God,so they cannot ever come to the truth.
A doubtful mind has a chance to come to the truth,but a mind that is set on not believing,nothing wavering,they will never come to the truth.
The only way they will come to the truth,is if something happens that starts causing doubt in their mind,but will God show them after He turns them to a reprobate mind,and an adulteress and evil generation require a sign,and blessed is He that has not seen Jesus and His miracles but still believes.
If they are turned to a reprobate mind,which means God is not working in their life and all they see is the flesh,which in the flesh dwells no good thing,then they will have to come across that doubt by mere chance.
They can come to the truth,but it will be harder than a person who has doubt,but not firmly set on not believing.
That is why the world will eventually go to the beast system,for more people are being turned to a reprobate mind,and will God show them a sign so they will believe,when an adulteress and sinful generation seek a sign,and the Bible says that the last generation before Jesus takes over the earth will be the most sinful generation of all(Proverbs 30:11-14).