Answer:
because the issue of slavery became much of a concern later
Step-by-step explanation:
Remember, a major cause of the civil war was the fight against slavery. At the time when the war broke out on April 12, 1861, there were very high tensions over putting an end to slavery.
However, at the time the Founding Fathers founded the United States some 84 years earlier on July 4, 1776, by drafting the Declaration of Independence the issue of slavery wasn't as hotly debated during their time. In fact, even some of them (such as Thomas Jefferson, George Washington, and James Madison) owned slaves, but little did they know that one of the primary reasons for a Civil War would be Slavery.