It’s not just that; it’s that much of what needs to be reformed simply cannot be done through an amendment; it’s either impossible in a practical sense, or impossible because the Constitution itself disallows it. One problem is the equal state representation in the Senate. It was never a great idea (and it is significant that both Franklin and Madison didn’t like it one bit), but in 1787, the “small states” not only managed to get that protection of their power written into the Constitution, they also somehow managed to get a clause inserted into Article 5 (which deals with the amendment process) “that no State, without its Consent, shall be deprived of its equal Suffrage in the Senate.” (That was tacked onto the clause which forbade any restrictions on the international slave trade before 1808, which makes me suspicious that it was something that got thoroughly debated. Or that if anyone objected, that one of the small state representatives stood up and said, “See? See? They are going to start chopping away at our influence the minute this Constitution is ratified! We cannot trust them!”)
The Electoral College is not so baldly protected, but does anyone think that we could get 3/4 of the states to vote to ditch it and go with popular election of the president?
It will take a new constitutional convention to clean up the worst of the problems, and I have little faith that people who have the wisdom, the judgement, and the devotion to civic duty of Benjamin Franklin or James Madison or Alexander Hamilton are going to be the ones appointed to be in the room this time around.