So why did every non-slave state add the right to bear arms to their state consitutions?

[hack89]

the slave states were going to violently suppress slave revolts regardless of the 2A. They were going to deprive AA of their civil liberties regardless of the Bill of Rights.

This may have been a factor in the 2A but it not the only or the largest. In New England, King Philips war was a larger factor than potential slave revolts in far away southern states - the need for armed citizen militias to defend hearth and home was a recent and bitter memory.