There's no rain, our crops have died from too much heat.
Killed off from Native American attack's
THIS LAND BELONGS TO US!
There was a possible drought, and that could led to a loss of all crops. Which also could have led to the starvation of the colony.
A hurricane could have devastating effects for the colony. After experiencing their first hurricane they may have decided to leave so they would not have to experience a second hurricane.
When White left on his journey, Native Americans may have came in and had done a surprise attack on the colony, and since the colony had no plan from the beginning, there was a small chance of them surviving the attack.