In the book "Bows and Arrows of the Native Americans" Jim Hamm goes on to say that "My conclusions about the rib bow are less charitable than those about the buffalo horn bow. Although the bone will make a bow, it is almost more trouble than it's worth. The advantage of the composite bow, the tremendous overdraw, does not exist with the rib bow. The rib bow is indeed a novelty, as there are probably not more than one or two others in existence, but the time and effort put in to it could be more profitably used to make a good sheep or buffalo horn bow".
Maybe the bone of the ribs is not as elastic or possibly heavier than either buffalo or sheep horn?
Alan