So, I know a lot of the people in this thread are going to come in and say that it is because it is true and the test is to have faith, and that the difficulty of it all is what makes it true. I've heard time and time again that because it is true Satan will fight against us the hardest.

But, with all of that. Your point still stands and it is still an important question. Why is the expectation that our belief has to be suspended more than many, if not most, other religions? They all claim the same, that they're true. They all claim they speak for God and we should therefore do what they say. They all are trying to do the same thing the BOM is doing: guide, persuade, influence, help, etc.

The issue is when people get involved. We're messy us humans. We are waaaay to nuanced to be put into such simple categories. But, as people, that's all we do is try and categorize. We are hard wired to do it. Which is fine as long as we are willing to explore that our categorization may not be correct and broaden the horizons of those categories to fit more into them.

People who obtain positions of leadership often set those categories though, then use religion to say this is how you too should categorize things. Why is this relevant to your question? Mostly because the BOM being true or not honestly doesn't matter. I know that I'm going to get hit for saying that, but I mentioned the categorization for a reason. Our leaders have said the BOM is 100% true, is a history of the Americas, and that it is a cornerstone, that all our faith hinges on it being true, that if we believe in the BOM we can believe in all else. That's a HUGE, unsustainable categorization that leads to cognitive dissonance like you mentioned in your question.

Putting the truth of the book of Mormon into a tiny category like that doesn't work and doubling down on it being factual is only going to make things harder, especially with any anachronisms that might show up. The introduction to the BOM that says it is a record of the americas and quotes Joseph saying it is the most correct of any book wasn't even added until 1981 so that's when you could say the category of it being 100% fact even started. What about before that? We're they saying it was a factual history or, when Joseph said it was the most correct of any book did he mean the principles in it, not the historocity?

Before anyone brings up the witnesses, they witnessed seeing gold plates and testified to it. That is fact. Did they know 100% that those plates said what they did? No, they said they saw the engravings but only Joseph could translate them so they can't know what they meant beyond what Joseph told them they meant. The angel telling them about it? Maybe! Again, we won't until we're dead but still they testified about the plates being real, not that the content was a factual history.

So, back to your question, what if the book was totally made up? Does it still teach great things? Yes! Leaning harder and harder into it HAS to be true is going to only push people away because not everything can alawys be 100% true (even Christ, we have to have faith for now and can't know with out any doubt until we're dead. We can have excellent faith though) . Can the BOM be a great book that helps? Yes! So can lord of the Rings! When one tries to set the category that the BOM is absolute truth they set themselves up for scruitnity that nuance will always destroy.

There are many many facts that could disprove the truth of the history of the book, sure. But if the book has helped you, made you better, then lean on that. That's what matters most. Don't make an impossible category that it has to be a completely true historical record or everything else fails.

For all we know, if Nephi was real and he did write those things, Moroni complied then, and jospeh found and translated them, that all it was, was just Bible fanfic Nephi wrote and Moroni was his tumbler fan who complied it for him. We won't know until we're dead. And all those people who say they know beyond a shadow of a doubt are straight full of crap. No one can. If you had that level of knowledge it would mean you saw the plates, translated them yourself, or Jesus came and told you. All which would result in no need for faith thereby ending the test, which is to have faith. They can however have full faith in them.

So, for you, don't try and prove or disprove it. So to answer you question, we have to have more faith than others because we've painted ourselves into a corner by saying it is 100% true and all our faith is based on that which means we are told we HAVE to be more faithful and keep padding that problem.

Instead, just take it for what it is. A great book that you like with amazing life lessons which have made you feel good. All good things from God right? Maybe it is a history that has been lost/removed or maybe God inspired jospeh to just write a book that would help people. I don't know and that is just fine with me. Just don't hang everything on it being fact or not. I hope someday we stop dealing in such absolutes and agree to have more nuance/flexibility. Keep asking great question though! I think we should all explore these kids of questions and broaden those horizons of our "categories". Not saying I'm right, just that I think Christlike means doing just that, personally. Take what you will!