Answer:
As people migrated to North America from Great Britain, they brought their pastimes with them and redeveloped them.
Explanation:
While it is possible the two games might have developed separately from one another, it is more likely that when people from England, Ireland, and Scotland moved to the United States that they would bring their games with them as well. Once America won its independence from the United Kingdom, baseball and rounders developed separately from one another. This explains why they are similar but different.