Simply put, the Constitutional Convention almost didn't happen, and once it happened, it almost failed. Even after the convention succeeded, the Constitution it produced almost failed to be ratified. Just as importantly, the Constitution was hardly the product of philosophical reflections by brilliant, disinterested statesmen, but rather ordinary interest group politics. Multiple conflicting interests had a say, from creditors and debtors to city dwellers and backwoodsmen. The upper class overwhelmingly supported the Constitution; many working class colonists were more dubious. Slave states and nonslave states had different perspectives on how well the Constitution served their interests.
Ultimately, both the Constitution's content and its ratification process raise troubling questions about democratic legitimacy. The Federalists were eager to avoid full-fledged democratic deliberation over the Constitution, and the document that was ratified was stacked in favor of their preferences. In terms of substance, the Constitution was a significant departure from the more democratic state constitutions of the 1770s.
https://www.amazon.com/Framers-Coup-Making-United-Constitution/dp/019994203X