Question

why did spanish plantation owners in the west indies begin usine enslaved africans instead of enslaved natives

Answer 1

European diseases had killed much of the native workforce.

Step-by-step explanation:

Answer 2

The natives didn't have immunities to Old-World diseases such as smallpox and malaria. Over 90 percent of the native population either died from the diseases or simply ran away and hid in the jungle.
Africans, on the other hand, possessed the required immunities.