There were a number of reasons. For one thing, the winters in Jamestown were notoriously harsh, and many settlers died in the biting cold weather. In fact, more than half of the original settlers died during their first winter in the colony. Jamestown was primarily a business venture rather than a settlement. Those who made the long journey across the Atlantic were there to exploit the New World's mineral wealth, not put down roots. As such, the practicalities of survival tended to be ignored. When colonists arrived in Virginia, they were often ill-prepared; they lacked the vital farming and building skills necessary to live off the land. The resulting starvation was as inevitable as it was tragic.
In addition to cold and hunger, potential recruits to the colonial venture were put off by bloodcurdling tales of the supposed violence and savagery of the indigenous tribes. Europeans didn't know much about Native Americans and what little they did know wasn't very reassuring. For many prospective colonists, no amount of gold was worth undertaking such a perilous journey only to be subjected to constant murderous assaults by what they regarded as wild, heathen savages.