Because the colony became succesful thanks to the cultivation of cash crops, particularly tobacco.
Explanation:
The colonists were few, and some of them were not willing to to hard work (they were upper class). This created a shortage of workers that naturally increased labor demand.
This demand was met with the arrival of thousands of indentured servants. Indentured servants were poor European immigrants who paid for their trip expenses with unpaid work in the plantations for a few years.
After their debt was paid off, they became free, and could become landowners themselves.
