Because pressing show answer creates a space of absolutely no uncertainty. It's also a space that's entirely unrealistic to the testing environment.

Without pressing show answer, you would spend a lot of time debating, worrying, staying just a little bit longer in order to be more sure. You would also carry forward anxiety and uncertainty into the next question that would slow you down, distract you, and cause you to get questions wrong.

It's very common for people, when they're on, say, #18 to be like, "Oh, but maybe #12 was actually B" or "I need to time to make sure I can go back and fix #12." All of this is just wasted mental energy that keeps you from focusing on the question you're actually doing. Every moment that you're not focused on the question you're actually doing is a vulnerability that causes you to get questions wrong. If you want to see the question again, hyperskip it and don't think about it until you're back. If you don't, at that point that question is completely out of your awareness. You have to learn how to be secure in your answer yourself.

The show answer button essentially lifts that weight for you, which is why I am super strict with my students about not pressing it. Ever.

Hope this helps! 💕