Noah tried to tell them...
Noah warned the people that God's judgment was coming. It took hundreds of years to build the Ark, and everybody knew why Noah was doing it. But nobody believed him until it was too late.
The Bible says in Luke 17:26 that "As in the days of Noah, so shall the days of the coming of the Son of Man be. People were eating, drinking, marrying and being given in marriage up to the day Noah entered the ark. Then the flood came and destroyed them all."
Don't wait too long. Once the door of the Ark was sealed shut by the hand of God, there was no hope of salvation for those who were outside. The same will be true of the Tribulation.
I wonder how many people repented to God, and asked forgiveness - as they perished in the waters?