The most accurate reason for the largely unsuccessful attempt to enslave the Indigenous peoples of the Americas in meeting the labor needs of plantations is:
European colonizers’ cruelty, as well as the spread of disease, meant that many Indigenous people died. As a result, there were not enough people left for colonizers to enslave.
When European powers colonized the Americas, they brought with them not only a demand for labor but also new diseases to which the Indigenous peoples had no immunity. This led to catastrophic population declines among Indigenous groups. In addition, the harsh treatment and brutalities inflicted by colonizers further decimated Indigenous populations. As a result, the combination of disease and violence left the colonizers with a severely diminished pool of potential labor, making it increasingly difficult to enslave enough Indigenous peoples to satisfy the labor demands of their plantations.
This situation eventually led to the shift towards the transatlantic slave trade, where European colonizers turned to Africa to fulfill their labor needs, resulting in the importation of enslaved Africans to the Americas.