Because google has all the answers? You know conflicting information is presented. It boils down to whom you accept as an authority.
So he drove out the man; and he placed at the east of the garden of Eden Cherubims, and a flaming sword which turned every way, to keep the way of the tree of life.
and then read chapter 4, we see a family of farmers and their family tree. They argue, one kills the other, there is a legal system in place that requires the death penalty for murder and he runs away to another land where there are more people.
Obviously the Adam family are not the first family ever, they have laws, there are other people, and a lot of time has passed between this and the end of chapter 3.