Skynet didn’t invent a time machine to kill John Connor. That was a misconception by the human resistance, which lionized its wartime leader and believed that its enemy must, in turn, demonize him. This is a misconception born of hubris; the human resistance believed that its machine enemy thought like a human, that it thought in human scales and had human desires. They forgot that Skynet is, fundamentally, a computer virus. And a virus has only one goal: reproduction.
The resistance believed that Skynet devoted its existence to wiping out what was left of mankind, but in truth, Skynet devoted merely a fraction of its processing power to eliminating the most immediate nuisance. This isn't to say that Skynet did not want to dispose of John Connor; it certainly saw the benefits in doing so, and it did devote some resources to the task. But Skynet could have done more. It could have sent more than one Terminator unit at a time, it could have sent a bomb covered in mimetic poly