I meant to point out in the “King James” thread that one reason they use these ancient translations, in spite of their shortcomings, is because they are in the public domain, and can be published without any restrictions. A biggie is that they don’t have to support the ongoing research (i.e. pay). There are other stump-jumping backwoods churches that print their own versions, or abridged versions, of the King James Bible for similar reasons. For example, (sadly) a friend’s wife attends an independent Baptist church that prints their own bibles, and they just leave out the parts that their preacher doesn’t approve of. For example, she says things like, “James has no ‘authority’,” whatever that means.
Just like the KJV uses archaic English, which somehow makes Mormons believe in it even more, the Italian Diodati Bible version uses archaic Italian. It's like reading Dante, or something. When I was on a mission to Italy in the late 1960's, we had maybe three versions in use, because no one had stipulated which to use. But the Diodati version became more and more popular among American members in Italy, precisely because it is more difficult to understand than something in modern Italian.
I've talked Bible with my very TBM sister, and she loves the KJV because it's in archaic English, and so therefore is more "meaningful" when read (according to her), even though I pointed out that no one understands very archaic things, like "...wist ye not..., or old conjugations of verbs, and use of nouns that have to be explained to the class right when you're in the middle of a quote. As for the churchc, I think that it also gives LDS, Inc. two things: 1.) Since one quarter of the BoM was lifted verbatim from the 1769 KJV, Mormons have to use the KJV in order to prop up the BoM; 2.) simultaneously, it also gives them an excuse to call out "mistakes" in the Bible, which gives them a convenient escape each time that the Bible doesn't support the Mormon doctrine, so that "...as far as translated correctly" becomes a real handy tool when a doctrine or belief isn't supported by the Bible.