Why should more than 28% of Americans be scientifically literate? Most people aren't capable of scientific understanding and most people probably shouldn't even consider college [if colleges were what they used to be].
And there's nothing wrong with that. It's just that our benighted public education system has, from the beginning, been given the impossible task of educating everyone -- even those who don't want an education and those who aren't educable.
All we've accomplished by insisting on educating everyone is to dumb the whole system down to the point where we barely educate anyone. And provide a lot of well-paying jobs for teachers, too, of course.