It may have been the WEATHER that did them in. Researcher Julien Riel-Salvatore says, "It’s been long believed that Neanderthals were outcompeted by fitter modern humans and they could not adapt. We are changing the main narrative. Neanderthals were just as adaptable and in many ways, simply victims of their own success."
Researcher Michael Barton agrees and says, "Neanderthals could have disappeared NOT because they were somehow less fit than all other hominins who existed during the last glaciation, but because they were as behaviorally sophisticated as modern humans."