The framers separated the U.S. government to limit the power of the federal government. The three branches on top of being in a "more weakened state" would also have a system of checks and balances which further ensures that one branch would not become too powerful. This system has deteriorated over the years, as the executive branch has gained immense powers that can bypass Congress, but the system is still in place even today.
The Framers structured the government in this way to prevent one branch of government from becoming too powerful, and to create a system of checks and balances. Under this system of checks and balances, there is an interplay of power among the three branches.
