Joseph Smith was COMMANDED by GOD to re-translate the KJV bible to get rid of the errors in it.
He did, and it is known as the JST: Joseph Smith translation.
For some strange reason; SLC does NOT consider IT to be SCRIPTURE, and chooses instead to use the fault KJV.
I have NO idea why this is so...
Because Mormonism is itself an entirely absurd and contradictory religion. If it could make sense, it would not be Mormonism.