Why did the Continental Congress make federal government weak when it drew up the Articles of Confederation?

The Articles were designed to meet the requirements of the Revolutionary War, which they did. The states at that time were highly independent and wished to preserve for themselves more power in deciding state issues.

The AofC is a short document. Read it. In its succinctness it shows that the Founders had only a temporary solution in mind for government. The Constitution is the next step in their government creation.