1. Indentured servitude of Africans was replaced as slavery that was heavily used in the south for labor in the plantations. British massively has to comply with the demands of more slaves in the turn of the 18th century.
2. Those who are slaves on shops had become an apprentice to the masters which made them develop their skills which are marketable for work.
3. Personal comfort for having household slaves. They were used to prepare food, attend to their master's needs.
They were needed to employ different tasks and to comply for faster work outputs.