How would there be a historical record of a community that killed itself entirely? Also, all these historical examples occur in the context of having millions

How would there be a historical record of a community that killed itself entirely? Also, all these historical examples occur in the context of having millions of acres to roam, probably access to a lake or ocean, sunshine, fruits, seeing other animals, and so on (the natural habitat of humans). Even in prison they get yard time, and prisons are extremely violent. The number of generations it would take to travel ### lightyears away is so high that _something_ is just bound to happen. What if one of the generations gets hooked on bath salts? What if they get irradiated and lose fertility? What if they start a cult? What if there's a lone wolf killer who takes them all out?