Answer:
Because of the high mortality rates, owning a slave for a lifetime was not as convenient as indentured servants.
Step-by-step explanation:
American Slavery, American Freedom is a 1975 book by historian Edmund Morgan. Using archival records, Morgan studies the contradiction between the political positions of Virginia in defense of freedom, and its status as the largest slave state in the United States.
When describing the transition of Virginia towards a slaveholding society, Morgan points out how despite the seeming convenience of slavery, plantation owners originally prefer indentured servants: "Because of the high mortality among immigrants to Virginia, there could be no great advantage in owning a man for a lifetime rather than a period of years, especially since a slave cost ronghly twice as much as an indentured servant. If the chances of a man's dying during his five years in Virginia were better than fifty-fifty -and it seems apparent that they were- and if English servants could be made to work as hard as slaves, English servants for a five-year term were the better buy." (1975, pp. 297-298).