Why is a second origin account given for man (Gen 2:6)? And are these accounts consistent?

There is nothing inconsistent about them, but there is a difference of emphasis. In Gen 1 we have an account of God’s creation, and man is brought up strictly in that connection. How he is made is not the focus. Gen 2, by contrast, is not primarily an account of God’s creation but instead concerning “the generations of”—that is, the family of—“the heavens and of the earth.” The focus, moreover, is on that offspring, namely, Adam and his immediate family. Gen 2 kicks off a string of “family stories,” beginning with the very first one. Gen 1, by contrast, is sui generis, because it is about the original creative activity of God, which happened once only and so is treated separately. That there is overlap makes sense, because the events are interrelated, just as there is overlap (and consequent repetition, as we will see) between the later family stories.