Satire pokes fun at what is happening right now; it's not predicting anything. Just like 1984 warned of the dangers of totalitarianism that was already happening, Idiocracy was about current U.S. culture at the time. It wouldn't have been funny if our culture weren't already like that 20 years ago.

The premise is just a silly one so that there's a plot-based reason to show an exaggerated version of what was already happening culturally. It's not intended to be the point of the movie.