All deadly sins that we know of and again the flood could have been a natural fluke that no Deity had anything to do with, but the limit minds thought because of that civilization sins they were destroyed for their sins...
Also Angels and Humans were mixing is one story that I remember, so maybe there is something about intermixing that they believed caused the Flood...
We know today the causes of natural disaster; that God (or what people were doing) did not start them. People don't change much. I find quite interesting that today when people notice a change in climate, we are still quick to blame ourselves...for something that has occurred from time immemorial.
While Noah lived before Abraham, down through the ages Rabbis have noted that in this particular account, Noah said nothing. To anyone. In a later time, Abraham asks God not to destroy two cities, but Noah says not a word. Not before the flood. Not during the flood. Not until well after the flood. When he curses one of his sons.
People then (and later) believed words have power. Words can do damage, so Jews have always been taught to be careful of what they say. A popular story (still heard today) is that a man said some bad things about someone else, later regretted it, and wanted to make amends. He went to his rabbi and asked for advice. The rabbi told him to buy a bag of seed and spread it in an open field, then return in the same amount of time it took him to want to make amends for his words. The man did this, and the rabbi told him to go gather all the seeds he had spread. The man blurted, "But that is impossible. I cannot possibly find all the seeds--and by this time some have sprouted..." (The same is true of words.)
In the story, God chose a man of very few words. He said nothing, a righteous man. (The contrast was the words of others were causing damage on the earth.) Noah spoke, cursed one of his sons, causing strife to build between that son and all the others--strife and wars that lasted down through the ages. One curse...and ages of strife between Noah's descendants.
The purpose of this story was not to teach man how mankind survived the flood, but how even new beginnings can be destroyed by a few words. (Notice that it was the son's own big mouth that caused Noah to curse him.)