Well it's also a glimpse at the change of the times in a way that mirrors the zeitgeist as a whole. That's kind of a hard medium to find, something that can accurately describe the "average" political views of any given period of time without introducing their own biases. But the Simpsons especially put a template on it, even if accidentally, since the goal was to create a no-less witty commentary on modern politics that the vast majority of the audience would accept.

To be clear, biased and politically skewed adult cartoons are everywhere and have tried, and invariably failed, to create an alternative narrative, because they're trying to form that zeitgeist instead of tapping into it. Ironically, Family Guy may be this type of person's means of grounding themselves, politically.