That's a great question! The reason why questions/practice tests are emphasized over reviewing the material is simply that the MCAT isn't a content-only test. I've seen so many people who know the science inside and out and still do poorly on the test, and just as many who aren't familiar with every little detail yet do awesome. The MCAT is all about interpreting the passage and questions and applying some piece (or pieces) of knowledge to what you're reading. Often, the question isn't straightforward, and it's difficult to tell what, if any, piece of information you should use. Just pulling from random example here (I won't mention specifics so I don't spoil the questions), the AAMC really loves to test springs in unconventional ways. I've seen passages about an oscillating sea of electrons, weird protein stretching, and a lake that is rising and dropping in water level. In all of those cases, the questions ended up simple if you used a little bit of knowledge about spring constants, PE and KE, etc. But many people only knew springs like they are presented in prep books or textbooks, and had no clue what was going on.
In other words, you need to become familiar with the way the AAMC talks. Back to your original question - how? First of all, don't just review the questions you miss. Even some right answers might have been the result of lucky guessing, after all! Look over every question and ask yourself a few things. First, is the science content involved familiar, or are you still uncomfortable with it? If the content seems ok, what additional reasoning did they use to get their answer? Did you use the same reasoning, or did you try something different? If so, that could be fine - the explanations sadly often neglect to give the most logical way to answer a question! But if not, why was your reasoning wrong - was it something that would've worked for a different type of question, or did you fall for some kind of "trick"? Did you read a graph incorrectly (since graphs are one thing that truly cannot be mastered just by reading the material)?
At minimum, I always advise writing down a sentence of more describing why you think you missed the questions you did. Don't rely entirely on the explanation here - again, they often give more info than you actually needed to solve a question. In fact, if you can, try to figure out what you did before reading the explanation at all. It's also super helpful to keep two additional lists - one of content areas that you need to work on, and one of your "dumb mistakes." Many people make the mistake of looking through the exam too quickly, noticing that they seemed to make a small / silly error, and moving on, saying "that was dumb, I won't do that again." But the truth is that there are very few genuinely stupid mistakes, and the rest are things you would likely fall for in the future. Just keeping a list that says "I forgot to convert to the right units," "I read this specific type of graph backwards," "I used the wrong signs for the electrodes on an electrolytic cell," etc. can remind you that you could easily see such a tempting trap on future tests.
Hope this helps! I'm looking forward to seeing what other people say about this as well. Good luck 🙂
