The fact that few if any humanoid style terminators exist as Judgement Day occurs perhaps can help explain some of the machine strategies in the future. If humans live in shelters deep within the Earth why would it be effective to sneak terminators into them and then shoot them all? Why not just use a bomb sneaked in by terminators or via explosions? Perhaps in the early days humans were rounded up rather than being killed on the spot because humans were needed as laborers and humans are more willing to die if its in quiet and not on ths spot. This need perhaps created the whole machine planning stategy of sneaking into underground settings to capture humans and kill them on the spot via shooting only if necessary. If machines change their strategies very slowly then as the labor need was no longer present they might keep the same attack strategies that gained them their laborers in the first place.

The illusion of hope is important to humans. Perhaps in early battles machines could promise food or other things and largely have the humans walk themselves to convenient extermination camps. Kyle Reese seems to talk of such camps a lot in Terminator 1 that ran night and day. A need for labor coupled with a need for raw resources might explain why there aren't more nuclear attacks in the vicinity of where human survivors are. If resources are plentiful why send troops out to hunt humans one by one? Just move the machines out and nuke the whole area. This would be logical unless the machines lack nuclear weapons and raw resources or the machines believe they ultimately are superior and that the resources that can be gained from inferior human life is worth gathering up. Lose a few machines in battle to ensure full utilization of available organic and chemical resources in the future rather than nuke entire geographic areas and wipe out humans and resources with no machine loses. This reasoning strategry might be the real reason for large scale conventional machine forces in the war including the terminator.