It's more of a spiritual gesture than some hard law. They aren't called "standardized tests" because they test for the exceptional.

I'm sure we can put the relevant education board in a room and have them argue over what should/shouldn't be on such tests, but the current result is a compromise after years of deliberation, being tweaked a little each year.

I'll be a bit more specific and say "high school testing is designed to provide a floor of knowledge a government feels its citizens should achieve" if that helps.