Why did James Madison invite the thirteen states to a meeting in the fall of 1786?

Even before Shay's Rebellion, prominent Americans were thinking of a means to strengthen the Articles of Confederation. James Madison and others met with George Washington at Vermont in 1785 to discuss commercial issues relating to Virginia and Maryland. In 1786 several state delegates asked if they could discuss the alterations of the article. only 5 sent representatives in fall of 1786. Since so few of them could make it, they resent the invitation for a hold of the meeting in Philadelphia, spring of 1786, when it was forwarded to the Continental congress.