How would the fall of the Eastern Roman Empire benefit traders in Africa?

Traders were not bound to trade with the Byzantine Empire.

Explanation:

During the rule of Justinian, the Empire main goal was to restore the glory of the Roman Empire. Byzantine Empire started taking territories in the west, which once were under the Roman Empire. Justinian first sent troops to North Africa to reclaim Roman lands there. Trade merchants from around the world travelled to the empire's capital Constantinople. Goods from the Middle East, Africa, India, and China transported.

With the rise of the Muslim Empire, northern Africa came under their control. In 711, the Umayyad caliphate invaded Europe, and by 720 Spain and Portugal were under Muslim rule. Traders focused on selling their trade in these regions as the Byzantine Empire began to crumble as its neighbouring empires began to grow stronger.