How did the system of administration of the conquered lands differ from the Arabs from the same system of government

How did the system of administration of the conquered lands differ from the Arabs from the same system of government among the Franks? What are the reasons for this difference?

The Arabs adopted ready-made systems of tax collection and administration from the powers they defeated (Iran, Byzantium). Being merchants and townspeople, they understood this economy and could learn its higher skills. On the contrary, the barbaric Franks did not know how to collect taxes and manage cities, which is why their conquest led to the collapse of the urban economy in Gaul.