yeah because none of these research studies have looked at children who are genetically at risk for stuttering (eg. because it runs in their families), before the onset of their stuttering. If they found differences in the brains of some of those children, and those would later begin to stutter, it would be proven that brain differences are causative for stuttering. Actually, there is exactly one such study from 2022: „White matter connectivity in neonates at risk of stuttering: Preliminary data“.