The Book of Mormon is a collection of writings from different authors. This means that if it were a true book, the writing style of each author would be different from each other and different from Joseph Smith.
Therefore if Joseph was the sole author of the book, he would have needed to fake many different writing styles, all different from his own, and not be detected.
While historically it may have been easy for an author to remain undetected, modern statistical and computational techniques are able to detect subconscious linguistic patterns and identify the actual author. A famous example was J.K. Rowling being identified as the author of The Cuckoo’s Calling despite using a pseudonym.
Recent wordprint studies have found that the Book of Mormon does indeed contain different writing styles for each author, which are different to Joseph’s own writing style. In fact, one peer-reviewed wordprint study by John Hilton and Berkeley colleagues (who are not members of the church) found that there is a 1 in 15 trillion possibility of Nephi and Alma being the same author.
Would we expect Joseph with his limited education to be able to mimic so many different styles of writing? Wouldn’t we expect wordprint studies to have exposed Joseph if he was a fraud?