The main question that these men had to think about was how centralized of a government they wanted and how powerful they wanted that government to be.
As you say, these people had just fought against a central authority that, they thought, had abused their rights. So now they had to decide how weak to make their own new government. They did not want to make it very strong because they had hated the strong rule from faraway England. But, on the other hand, they needed some sort of real government that was not too weak.
As it turned out, they created the Articles of Confederation and then, by 1787, decided that those created a government that was too weak and decentralized. That is why they went back and created the Constitution.