The United States has had 44 presidents. The quality of the presidents has ranged from very poor to slightly good, but most of them have been poor; they have just muddled-through.
Why is their performance rated poor? None of them made significant progress in solving/resolving major problems/issues facing the United States.
Why have these presidents failed so badly? This is the big question. The answer is simple. They were all politicians. All politicians can do is get elected, feed their egos and look out for themselves.
And the worse of it is that there is no change in sight.