[hajile]

These pronouns were adopted by groups like the Quakers for a long time after the KJV was made. they didn't refer to a single person with "you" because it is a kind of "royal we" where you ascribe plurality to a singular person (when they believed that only applied to God).

When the KJV uses thou or you (it uses both depending on plural vs singular pronoun references), that is because the underlying text is implying something different. Translations without this distinction are losing some of their meaning.