Question: Why does the writing style of the book of Moroni differ so dramatically from the style used in the book of Ether?
Answer: The main reason for the variance in writing style is that Moroni was the “abridger” of the book of Ether and the “author” of the book of Moroni. The book of Ether was written in a narrative style, whereas the book of Moroni lacks narration.
Another difference in styles is that Moroni used the phrase “and it came to pass” 117 times as he abridged the records of the Jaredites. In his own writing of the book of Moroni, the phrase is not used once.
Source: 400 Questions and Answers About the Book of Mormon by Susan Easton Black, p. 209.