Good point. Here are some observations I made about that subject a while back.
Noah's preaching
In Gen chap 6 God gave Noah very detailed instructions about building the ark. In 6:18 and 7:1 he gave specific instructions about who to take into the ark. No instructions were given to Noah about warning anyone that they too should get on board with him. Apparently, the judging had already been done and Noah was chosen to be saved because he was a righteous man.
Hebrews 11:7 shows that Noah built the ark 'for the saving of his household'--not anyone else. The Bible calls Noah a preacher of righteousness. However, it gives no indication that he undertook a global campaign to warn people of a coming flood of which they 'took no note'. So while Noah was a 'preacher of righteousness' this may refer to his preaching righteousness before the matter of the flood ever came up. This may have contributed to his being chosen to be saved.
Is it even practical that Noah could have set out on a global mission to get people into the ark? Did people on the other side of the world even know he was building an ark? Since the size of the ark had already been determined , did Jehovah really intend for other people to join Noah? Matthew 24:39------ and they took no note until the flood came and swept them all away. . .NEW WORLD TRANS
Almost any Bible you pick up indicates that people were not expecting the flood----not that were ignoring noah's warning. They didn't know it was coming. It is notewothy that the Kingdom Interlinear Bible published by Jehovah's Witnesses renders the Greek "not they knew" but the English "they took no note". Is there not a difference in not knowing something and taking no note of something you know? Other Bibles say: were unaware--knew not--did not understand--knew nothing about what was happening--didn't know anything was happening--knew nothing about what would happen--didn't realize what was going to happen--did not know--they knew nothing
This fits in perfectly with the context and the point Jesus was making. His point was that his return would come as a surprise; not announced beforehand. This becomes apparent by considering Luke's account. Luke 17:28 says "likewise" and compares the days of Noah with the days of Lot------sudden unexpected destruction as they were eating, drinking, buying, selling, planting and building. There is no indication of a warning work before the destruction of Sodom. Jesus said in vs 30 :"The same way it will be on that day when the Son of man is to be revealed". Do we not understand that day to be his coming at Armageddon?
Notice Kingdom song # 215 Extending Mercy to Others 1. When Jehovah decreed that a deluge Should destroy wicked men long ago, Then to Noah he gave a commission: ‘Build an ark! Preach the word! Let men know!’ Now, did Noah reject that assignment, Since he never had built arks before? No, but he made good use of God’s mercy, And he built and he preached more and more. Where in the Bible do we find this 'commission' to preach? Or that he 'preached more and more'?
(Luke 17:27-30) . . .. 28 Likewise, just as it occurred in the days of Lot: they were eating, they were drinking, they were buying, they were selling, they were planting, they were building. 29 But on the day that Lot came out of Sod'om it rained fire and sulphur from heaven and destroyed them all. 30 The same way it will be on that day when the Son of man is to be revealed.