Board Thread:Questions and Answers/@comment-5959298-20170221145233/@comment-27056410-20170420010157

My best guesses:

Black hole: Sam said that SG-10 would be pulled apart by the gravity. the people on 451 could have died long ago due to the gravity and due to time being really slow there due to gravity there's no telling how long it was there.

riots: the humans who lived there may have seen the black hole and thought it was the end of the world. The humans may have started rioting those killing everyone.

Starvation: the stargate was in a desert and on most primitive worlds they live neer the stargate. It stands to reason that the humans lived by a small river or pond. So not much food being grown there so they most likely got food from other worlds. But when 451 got to close to the black hole what happened to sg-10 when they dialed the gate happened to the native humans as well. With out the sorce of food they died.

Goa'uld killed them: The goa'uld may have killed them for fun, the black hole, or the humans where revolting.

mind you most of this is speculation some more likely then others I think it was the goa'uld or riots that did it due to hammond giving the info you gave above.