I figured that the AI were in the process of killing every single surviving human. But in countries without a large manufacturing base, or complex infrastructure, a large cache of weapons, or are isolated islands, the killing is much more methodical and effective. If you live in some third world country, and don’t own or have access to any guns or explosives, when the HKs show up, you can’t do a thing. Exoskeleton terminators just march from one side of the continent to the other and kill every last living thing. With nothing to stop them, and no time limit, no one can survive. You can’t use sharpened sticks and harsh words against terminators. By the time of the future scenes in the original Terminator, there may be no one alive in most of the world. Even the humans that have enough to put up a fight might be on the verge of going under, being outnumbered by the sheer amount of machines going after them.
It depends on how long the time frame is between judgement day and the human’s final defeat of the machines. Speculation again - after the initial attack, the machines didn’t have a manufacturing base set up. When humans started fighting back, they had tactics and bases more or less ready. The machines took a hit. Then the terminators were made. Infiltrators. The first ones had rubber skin. They were spotted easily.
By now the machines automated manufacturing is up and running. Soon even the survivors we see would be eliminated. Whatever JC did to cause the final defeat was never mentioned, but it must have been fast. They couldn’t sustain the losses seen in the future scenes for very long.
I guess, not more than two years between judgement day and T1? Less? Was it ever mentioned? (I never saw Salvation, and I don’t think Sara Connor Chronicles can be considered movie canon).