Family Chronicles
It is important at this stage that we dig into the literary nature of the book Genesis. It is essentially a compilation of what in Hebrew is 'elleh toledot': sections, each ending in the phrase which may be translated 'these are the generations of ...'. This phrase is really the title of the passage, to use title in its modern sense, so we need to adjust to the fact that the title of each section comes at the end of the passage, not the beginning, as we are used to. This is why the conventional chapter and verse divisions (a very much later addition) give the wrong impression.
The next section after 'the generations of the heavens and the earth' is 'the generations of Adam'; this begins at Genesis 2:4b and ends at Genesis 5:1a.
All the rest of the book Genesis is a compilation of similar sections, each ending in 'these are the generations of ...' till we finally get to 'these are the generations of Jacob' (Genesis 37:2a), after which we dive into the detailed story of his son Joseph, which takes us to the end of the book.
So after the family chronicle of Adam we get the family chronicle of Noah in Gen. 5:1b to 6:9a. This is almost entirely an archive of names (who was father of whom) and at the end only just mentions God's plan to remedy the wickedness of that region with a flood, from which Noah and his family would be saved.
It is in the family chronicle of one of Noah's sons, Shem, from Gen. 6:9b to 11:10a, that we get the detailed account of this flood, and some other events that followed it, including the multiplication of languages.
Then we have the chronicle that begins with Shem and is called 'the generations of Terah'. Terah was Abraham's father. This is a short archive of names, from Gen. 11:10b to 11:27a.
The family chronicle of Abraham begins at 11:27b and go on in much detail till 25:19a where it is described as 'the generations of Isaac, Abraham's son.'
The family chronicle of Isaac's son Jacob (25:19b to 37:2a) is another long narrative, and incorporates within it the family archive of Esau, Isaac's brother (36:1-43). After this chronicle we have the story of one of Jacob's sons, Joseph, which begins from Gen. 37:2b and continues to the end of the book.
So long as each of these family chronicles is read as such it is clear why there seem to be odd recapitulations. Often a new family chronicle begins by mentioning the birth of the person who has already been included in the previous chronicle. Noah's family chronicle, for instance, begins with Adam:
In the day that God created man, he made him in God's likeness. He created them male and female, and blessed them. On the day they were created, he named them "Adam". [Gen. 5:1b]
The chronicle then picks up the family of Seth and continues on from there, even though we have already met Seth in the family chronicle of Adam. It is only if we appreciate that these were originally separate accounts, independent of each other, that this can make sense. Genesis, in it present form, has been edited to bring all these original archives together, with no concern for repetitious recapitulations.