I have taken the ACT a total of 4 times and my scores continued to rise until my last test I took. 3 out of 4 of my scores had risen by a couple points, but my science had fallen by 6 points. I had received a 26 in the science portion in June, but received a 20 this time. I know that I can achieve a 26, as it shows I have done before. Why take the rest of the test when my scores are all around the same numbers but then my science jumps?
Why would they allow that? It's up to you to learn the knowledge and maintain it as life moves on. Doing what you suggest is essentially giving students a free pass. Achieving a high score the first time doesn't mean that is the score of testing that you will always get.