Originally it seemed as if this was the result of the Raiders scattering to rebuilt at the end of Commander Lilith, though Fantastic Fustercluck all but states it happened much more recently then that. The rest don't get a passing mention by those on Sanctuary either despite their reputation and previously tight bond, even after their friend and former leader, Maya, has been killed.
It only grows from there as the story continues and they begin directly opposing Hyperion by themselves.