This is all false. After Independence was declared, the shooting started. Pennsylvania didn't wait when it came to abolition. They abolished slavery in 1780, before the last of the red coated soldiers left. They couldn't wait to do it and didn't wait so that's falsehood number 1.
So yes, they did choose so. That's falsehood number 2. Several other states abolished slavery as well in subsequent years. Because of the resolve that the Founding generation had to abolish slavery beforehand, when the King wouldn't let them, abolition continued afterwards and that's exactly how we ended up with free states and slave states. These are direct results of the King. America did NOT choose that. Vetos have consequences.
"When they drafted the Articles of Confederation, they chose not to end slavery."
This is where the "by force" comes in. By vetoing abolitionist laws, the Empire inadvertently created this mess by ensuring that the only way 13 colonies could survive a fight with a superpower was to overlook everything and embrace Union first. Which is exactly what the Founders did. 1776 is always off the table as a date for abolition because with only 12 or 11 colonies(or even less) what you're left with is mass graves. Apparently you think mass graves might've been a more optimal result?
The struggle for freedom is usually never complete in one move. The Maroons in Jamaica did exactly the same thing that the Founders did. Cudjoe and his allies "freed themselves" and then they "came back for the slaves later". You do what you have to do when you're facing a superpower. You can't get everybody. That's impossible. That's reality.
The story of why 1776 could never be abolition year is contained in the cartoon "Join or Die" by Benjamin Franklin. 11 or 12 states couldn't overcome the Empire. The Empire's simple existence made it impossible. Furthermore, the Founders were so terrified of a tyrant having actually lived under one for so many decades, that the Articles of Confederation were expressly written to prevent that kind of national action from being truly pursued. If you would prefer to cast it in a cynical light, the Founders boxed themselves out. Living under a tyrant has that effect.
"When they drafted the Constitution of the United States, they chose not to end slavery."
I think you have a misconception of what the Convention actually was. This wasn't the U.N. This wasn't a meeting of all the dictators where they were going to get together and discuss the best ways to centrally plan society and plot and scheme against any who oppose them and should there be any opposition those with concerns will be shot or otherwise thrown into Bastilles and forgotten. You can't think the same way about the Founders as you would a progressive.
The convention was simply a discussion on how to frame government separately of society and nothing more. They did NOT come up with regulations to coerce people to live this way, they did NOT come up with taxes to force people to live that way, etc etc. What the Founders saw happening in society gave them much hope and it was exactly that: slavery was being rejected and abolished. Here's what was said on August 22nd 1787 about it:
Mr. SHERMAN was for leaving the clause as it stands. He disapproved of the slave trade; yet as the States were now possessed of the right to import slaves, as the public good did not require it to be taken from them, & as it was expedient to have as few objections as possible to the proposed scheme of Government, he thought it best to leave the matter as we find it. He observed that the abolition of Slavery seemed to be going on in the U. S. & that the good sense of the several States would probably by degrees compleat it. He urged on the Convention the necessity of despatching its business.
"From the day the last of the King’s soldiers left the 13 colonies, we, and we alone are responsible for the existence of slavery in what would become the United States of America."
Only with honest stipulations. I'm not seeing much of that so the statement does not stand alone as a simple statement of fact. It's false. Now maybe you didn't know any of this and that's ok, it took me a long time to pick it up. But your line of questioning so far has been nothing but ahah-gotcha.