How about as teachers?
How is someone with a college degree in computer science not qualified to teach high school computer classes?
How is someone with a college degree in mathmatics not qualified to teach high school math?
How is someone with a college degree in physics not qualified to teach high school physics?
How is someone with a college degree in chemisty not qualified to teach high school chemistry?
How is someone with a college degree in art not qualified to teach high school art?
Because none of these people have a degree in "education," which means they aren't allowed to teach anything at the high school level.
But they are allowed to teach college classes. If anyone ever took a college class from a grad student in college (and who didn't), then you took a college level course from someone "not qualified" to teach high school.
One of the top schools in Mississippi is a private school called St Andrews Episcopal School. 100% of its graduates go on to college, and alumni routinely are accepted to the Ivies, Standford, Duke, etc.
A few years back St. Andrews failed to be accredited by the state because of this issue — The physics teacher had a PHD in physics from MIT, but no teaching certificate, etc.
St. Andrews did not change its policies. It simply thumbed its nose at the state. Nicely done, I might add.