Why does Equiano blame the illness aboard the ship on the "improvident avarice" of the traders?

Taken from his village in what is now Nigeria, Olaudah Equiano was eleven when he was first captured. After six or seven months of captivity, he arrived at the sea and is horrified at the sight of 

...a multitude of black [sic] people of every description, chained together, every one of their countenances expressing dejection and sorrow....

When he is moved into the hold of the ship, Equiano is overcome with the "loathsome stench,"and when he cannot eat, he is flogged. However, because the stench as the "whole ships's cargo were confined together" the area becomes what Equiano calls "pestilential." The confining environment, the nearly suffocating atmosphere of being packed together, added to the sweating and eliminating of the slaves, effected the death of many of them. This deplorable situation was "aggravated by the galling of the chains" and the screams of women and shrieks of the dying. Children even fell into tubs of defecation.

The "improvident avarice" of the slave traders, their desire to pack in as many as they can into the hold, along with their failure to maintain sanitary conditions lead to the death of many of the slaves. Fortunately for Equiano, because he is so young, he is not chained and can move onto the deck where he can breathe and get away from the gaseous smells.