Why did the framers write the constitution?
While it can be argued that ultimately since all the states eventually ratified the Constitution this was a legitimate, amending of the Articles of the Confederation under the rules of the Articles. If 9-12 states approved, the Constitution would still come into effect in violation and the Articles rules forbidding any other alliance between states. One of the reasons for this is that 9 or more states formed their own alliance, the other states would become fully independent and lose the trade and defence benefits of the Confederation, and this put additional pressure on the last ratifying states.