Questions About Terminators

Here's my problem with the "Terminator" movies. Time travel is a terrific concept for science fiction, whether it falls into the "you can't change the past, only confirm it" camp or the "you can change the past and it'll have effects you can never anticipate" camp. The Terminator movies went with the latter camp--in the first film, the hero Kyle Reese went back in time to protect the mother of his boss (John Connor) from California's future governor (Gray Davis wasn't available, so they went with Arnold Schwartzenegger). As it turns out, Kyle impregnates Sarah Connor, making him his boss's dad and thus totally changing their workplace dynamic. But it raises a lot more questions, besides "what sort of weirdo pimps out his underling to go back in time to pork his own mother???"

The first question is, once the evil robots realized that their scheme didn't work--the Terminator did not kill Sarah Connor--then why, when they had an improved version of the Terminator for the sequel, did they not simply send it farther back in time to kill Sarah Connor when she was a child in the '60s? And again when she was snorting coke in a disco in the '70s? Or even ten minutes earlier than they tried in the '80s? The point is, with time travel you can keep it up infinitely. For that matter, when the humans sent their own Terminator to protect Sarah and a young John Connor from the new and improved Terminator in the sequel--in fact, they sent one that conveniently looked like Schwartzenegger as well! You'd think they could have made one that looked like Chuck Norris if salary negotiations broke down--why could they not send their protecting Terminator back to the time of the first film? We could have witnessed an infinite number of Terminators battling it out for eternity!

For that matter, why didn't the bad guys just send a Terminator back in time to kill a young Kyle Reese? Or the parents of Sarah Connor and Kyle Reese? Or the guy who invented poofy pants?