Final answer:
The cruelty described by Equiano suggests that the brutality of the crew on slave ships was primarily due to economic interests, aiming to preserve the value of their human cargo for sale and to exploit insurance policies.
Step-by-step explanation:
The information about Equiano's experiences and the accounts of slave ship conditions suggest the crew's brutality was largely rooted in economic interests, as indicated by the harsh treatment of enslaved individuals to maintain their market value and the extreme measures taken to ensure the profitability of the voyage by minimizing losses due to illness or death. The practice of sacrificing sick captives to claim insurance and the forceful exercise of the enslaved to appear healthy to buyers highlight the economic motivations behind the brutal treatment. This economic drive, combined with the dehumanized regard for the captives, resulted in the extreme cruelty described by Equiano and others.