Endless Warranty

We needed to return an electronic thermometer to Williams-Sonoma because it had stopped working about a year after we got it. Actually, it more kind of went crazy, switching between two temperatures and being completely inaccurate. The salesperson said that normally they only give out 90 day warranties for electronics, but I wondered why? I mean why would an electronic device fail at all ever unless there was a flaw in the manufacture of the device in the first place. So I say: why can’t every electronic device have an endless warranty, since no matter when it fails, it’s nearly always a failure in manufacture of the electronics?