What would most likely be the reason why there were few slave rebellions in the original english colonies in north america?

Fewer slaves and better conditions--The British were typically more lenient on slave laws and there were not as many slaves during the colonial period. 

Prior to the American Revolution, slavery was mostly limited to the Southern colonies in particular the Carolinas and Virginia. Slavery under British law was not as strict as it will become and there were often ways to buy freedom. Also slaves were expensive and production was slow. Slavery will increase in the newly formed US after the cotton gin is invented in 1794. This will increase numbers and make the laws more severe leading to more uprisings.