States are totally unwilling to impose objective standards on new (and existing) teachers because any meaningful standards would result in...no more teachers, or at best, almost no POC's teaching.
People who major in "education" (not actually a subject) routinely are shown to have the lowest incoming SAT scores of any major. In the states where they have tried competency tests for teachers, they invariably fail because Black and "Hispanic" teachers basically all fail the tests, so they have to be recalibrated into nothingness.
In a perfect world, teachers would have to demonstrate competency both in their subject area and in elements of teaching, and they would be paid handsomely. In a perfect world, there would be no shortage of science and math teachers because people with quantitative degrees could transfer into teaching for a period without the bullshit of having to waste a year studying "education" and student teaching, or start at the bottom of the pay scale.
In this as in many other things, the biggest obstacle to real reform is the teacher's union(s).
I have worked with companies headquartered in Germany, Austria, and other rational countries, and they have professional unions, in which the union works with the employers to maximize productivity and compensation. This model puts to shame the adversarial situation in the U.S. where the teachers' unions act like LABOR unions, fighting for the worst of their employers and screwing the taxpayers who pay their salary.