So the people making the changes were prophets or something? They had authorization from who/whom to make them? Still Joe wrote three different versions of the BOM translation.
I've read many different explanations for why the changes were made, as well as denials that changes were made, often in the same source.
As for how the Book of Mormon came to be, it was initially published with Joseph Smith, Jr. shown as 'author.' And the official drawings and paintings shown by the LDS Church show Smith reading the gold plates on a table and translating them; that version appears nowhere in history but only in the drawings. In written LDS history, Smith used either the Urim and Thummim in a breastplate, or his seer stone from his money digging days in a hat.
I'm not LDS. You would have to ask the LDS Church why it chooses to portray Smith as translating the plates, sitting open on a table, rather than sticking his head in a hat that contains an occult rock.