Maybe they could have. But they didn't. You bring up an interesting point. The profile you refer to is a duplicate of Nancy (Hanks-52) Lincoln, and much of the information it contains is wrong, starting with the opening sentence. DNA has in fact proven her parentage, at least as far as who her mother was.
The bulk of the profile, a paragraph starting with "All Hanks historians agree..." is flat wrong on most counts. For instance, no one "agrees" that Lucey Hanks died in 1792 (she married in 1791, and started a large family); no one "agrees" that Nancy's father died in 1793-- because no one knows who her father was. Nancy did go live with relatives, but it was Lucey's childless sister, Elizabeth Hanks Sparrow who took in Nancy, when Lucey married Elizabeth's brother-in-law. The one source cited in this duplicate profile, Adin Baber, has been proven wrong on many counts, including the wife of Abraham Hanks.
The point you bring up with your perfectly reasonable question, given the misinformation in this duplicate profile, is this profile needs to be merged away.