Mormon disobeys Ammaron

In the book of Mormon – by this I mean the book by that name within the overall Book of Mormon – the record keeper Ammaron chooses Mormon to be the next keper of the plates of Nephi and the other sacred records of his people. Ammaron has hidden these records in a hill called Shim. Ammaron tells Mormon:

And behold, ye shall take the plates of Nephi unto yourself, and the remainder shall ye leave in the place where they are; and ye shall engrave on the plates of Nephi all the things that ye have observed concerning this people.

Ammaron’s command to take the plates of Nephi is obeyed by Mormon, however, Mormon disobeys his command to leave the rest of the records in the place where they are in Mormon 4.23. Instead, he removes ALL of the records during his second visit to the hill. His justification is that the Lamanites were going to overthrow the land, but the same thing happens later when Moroni hides the records and God preserves them until Joseph Smith recovers them in the 19th century. All we know is that Ammaron commanded him to leave the remainder of the the records and Mormon disobeyed that command.

Book of Mormon – textual corruption

Let me assume for a minute that the Book of Mormon is true. A few questions:

Why was the BOM preserved intact when the Bible was corrupted? What was the difference?

How do you *know* that the BOM is any more uncorrupted than the Bible? What if the same processes that corrupted the Bible worked on the BOM? How do you prove or disprove this?

How do we know that the narrators of the BOM are honest? What if Nephi, Alma, Moroni, or anyone was dishonest and recorded legends and fables that never happened? How do you verify any of thi

I am asking a methodological question: why is one text “pure” and the other “tainted?”

What processes caused this to not happen to the BOM?