So that they can imperfectly be held accountable by all imperfect people. Now let us find a nice foundation of sand to build a castle on.
The whole point of checks and balances is to get good results from imperfect people. You can use the ambitions of one individual or group to hold the ambitions of another group in check.
I feel like you're just trying to be snarky and or gratuitously negative though.
Americans have deified their Founding Fathers to such an absurd extent that they seem to be unable to think critically. That maybe Hamilton and Madison were engaging in wishful thinking. That maybe the anti-federalists were right. That maybe Henry Clay's American System and his antecedent in Hamilton largely botched the ideal separation-of-powers republic from the beginning.
Granted, it uses an imperfect system of consensus to "do" this right now.