Can you be more specific as to what particular aspect of late antiquity you find most divergent?

Because on a cursory level, the answer to your question is analogous to "why do journalists give very different perspectives of this current time period?"

The final chapter of Bryan Ward-Perkin's "The Fall of Rome" gives a great answer to this question. Those studying the fall of Rome focus on material culture we can find in archaeology (of which there is a severe loss in quality) and focuses on the marked increase in violence we find in the written sources. Those studying Late Antiquity more broadly tend to study religion and intellectual traditions look at the continuity between Late Antiquity and the Early Middle Ages, as well as the similarity in government structures between the barbarian kingdoms and the Western Roman Empire, and thus conclude that there was a continuity rather than an abrupt change.