Here is one non scientific reason why the worldwide flood has no bearing even within theology.
Paul states that the whole world and all of creation has heard the good news in the first century.
Colossians 1:5-6
New American Standard Bible
5 because of the hope reserved for you in heaven, of which you previously heard in the word of truth, the gospel 6 which has come to you, just as in all the world also it is bearing fruit and increasing, even as it has been doing in you also since the day you heard it and understood the grace of God in truth;
Colossians 1:23
New American Standard Bible
23 if indeed you continue in the faith firmly established and steadfast, and not shifting from the hope of the gospel that you have heard, which was proclaimed in all creation under heaven, and of which I, Paul, was made a minister.
Now to him who is able to strengthen you according to my gospel* and the preaching of Jesus Christ, according to the revelation of the mystery that was kept secret for long ages* but has now been disclosed** and through the prophetic writings has been made known to all nations, according to the command of the eternal God, to bring about the obedience of faith…”* [Romans 16:25-26]
So was the gospel literally heard by the whole world in the first century? 2,000 years ago was the gospel already in Australia and the Americas? If not then he just have meant something different than our understanding of the whole world.