Yeah, see when the terminators were first created in the 80 (as a concept.) they were a folly of run away technology. They were... not impossible, but such a ridiculous long shot that it might as well be impossible.
But it's 40 years later, and the kids that grew up on the 80's super science fiction are now weapon developers, and military technology has already swung towards drones. We HAVE terminators, but the designers found the human form to be FAR to inefficient and unwieldy for serious and significant killing.