After the Roanoke incident, plans to launch another colony in Virginia started in 1606 when the Jamestown colony was formed nearby. This was the first successful colony in New England.
People were more inspired by the so-called "American Dream" and the American ideals of life.
There are a couple of reasons for why the empire didn't last. One of those reasons is that the empire was too great (big). Because the empire was too huge, it was divided into different parts after Alexander's death. He also didn't have an heir to the throne, so when he died, officials fought for power and to become king, which also contributed to the fall of the empire as well.