I don't have an exact answer but here is what I think: Considering how many different people there were, who established each colonies, (The Duke of York establishes New York, Pennsylvania is established by William Penn, etc.) Can you imagine how long it must of taken to find, all these different colonies, without it already being a colonized place? Considering everything was still new to these 'explorers' It takes a long time to establish something like colonies. Some of them were just founded, then established too.
