Against which reference would you test your teachers qualification? I would argue for that you need a standardized expectation of what teachers need to be able to do and therefore you will have a standardized curriculum for teaching teachers how to teach. You will have the same situation for electrical engineers, for doctors, for air traffic controllers...

So for all these people to be able to learn the standardized qualifications necessary to do their jobs reliably they need a standardized higher education. And that standardized higher education needs as standardized main education to build up on.

In my country we have state level curriculums. They are like 90% the same, but for some topics they aren't. This was causing quite a headache for instance in university with maths. Some people already knew some Linear Algebra from high school, others already had imaginary numbers and yet again others had learned their trigonometry with hyperbolic functions instead of the standard sine and cosine for some reasons. Would have been better if the supposedly equivalent diplomas from the different states actually were equivalent.