Bows died out...that what happend;-)
Nah Dragon is on to something....flatbows (including Holmegaard and Møllegabet) were superceeded by ELB's, which were superceeded by firearms. When bows came back in recreational fasion, peoples minds were imprinted with the imidiate middle-age history of archery...that, and "yew brain wash" by alot of authors;-). By the time bow artefacts from the stoneage were found, described and knowledge of them had slowly seeped into the minds of archers, the glasfiber-age had gained a steel grip.
In my parts of the world (denmark....not far from were the Holmegaard bow was found) Elm flatbows are a VERY rare sight indeed at 3D shoots and at the clubs/ranges. NO one knows about the "molly" design, or the actual artefact, and no one knows that the Holmegaard dig produced two bows. Hell, very few knows Elm is good bow wood....people continually ask if my bows are Ash and seem surprised when I tell em they are wych elm, and they allways give me that "huh, so you couldnt find yew, could you?" look;-).
Cheers