Because 13 men signed the Declaration of Independence
Because there were 13 delegates at the Constitutional Convention
Because the flag was first raised in 1813
Because there were 13 original colonies✓Correct answer
Official answer
because there were 13 original colonies
because the stripes represent the original colonies
Explanation
The thirteen stripes stand for the thirteen colonies that became the first states. The stripes have stayed at thirteen ever since, while the stars change as states are added.