For a couple of generations, we've all understood that the leftists (commies, socialists, etc.) were deliberately dumbing down the schools. Why, suddenly, do "conservatives" want to join in that left-wing effort, to destroy what little remains of the schools? There is nothing conservative about raising a generation of know-nothings.
It's not just a matter of knowing "nothing". *That* is easily remedied. But as the old saying goes, "it's not what you don't know that gets you into trouble, it's what you 'know' that ain't so."
And the creationist propaganda machine has been filling the heads of millions of people with vast amounts of things which simply "ain't so".