There are plenty people who are qualified for teaching children math. But it would be a disservice for them and their family to accept a low wage teaching job when they can work for $400k+ elsewhere.
Your argument is like hiring only minimum wage workers to build rockets, then complain that on average they don't provide that much value and can't solve integrals in their heads.
If we want better teachers, the solution is not surprising: pay more.
Just increase the numbers on the paychecks and the current bad teachers would all go away and be replaced by different, better teachers? Somehow, I doubt that.
I don't think you need someone amazing at maths to teach kids. In fact that would probably be detrimental for most kids.
I don't say that teachers don't provide much value because they're useless, but because they are usually very generalized and most kids don't seem be to that interested in learning.
Even if you fix problem #1, you haven't fixed the arguably bigger problem. I also don't think that significantly increasing the quality of teachers would change much for most kids.
I don't understand why everyone believes teachers are so undervalued. On average, I don't think teachers provide that much value.
My pet peeve is teachers teaching children maths. How can you teach something that you don't understand?