I don't know why, but you're missing my point. "Adam" was not "a people." He was an individual who lived 930 years and fathered specific individual children who are named, and whose children are named in turn.
What is so difficult about this?
While Genesis 1 desribes the creation of mankind, I agree that Adam was an individual, as was Eve. The story of their "births" is in Genesis 2.
Look at the first verse in Genesis 2:
Thus the heavens and the earth were finished, and all the host of them. All of the host of heaven & earth were created before God rested on the seventh day. If Adam and Eve were the only humans before the seventh day, would they be considered "all of the host" of earth? A host of two?
Genesis 2:7 And the LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul.
Adam was made a *living soul* after he was *formed*. Adam & Eve were the ancestors of those who later became God's chosen people, the (spiritual) lineage of life.
The Bible does not give us a specific number of children & it doesn't name all of them. Adam and Eve had Cain (Genesis 4:1), Abel (Genesis 4:2), Seth (Genesis 4:25), and "many other sons and daughters" (Genesis 5:4).
The Bible says that Seth was born to "replace" Abel. It doesn't say that there was an older sister who went to Nod with Cain & Cain had a wife. Cain's children are named, as are some of his son's wives. Were the wives of Cain's sons Cain's daughters or were they children of Adam & Eve, grandchildren of Adam & Eve through Cain's siblings? Other than Cain, why would any of Adam & Eve's children or grandchildren go out from the face of the Lord. Why would all of them share in Cain's punishment?