Its all about fighting for the right to operate without measurements. The only way they can sell their public education product is if there is no competition.

they're non-union and high performing

When I struggle to see the anti-competition view of school, the only thing I come up with is this: If we allow competition, the smart people will all go to the good schools, leaving behind the troubled people of the world. We want people with their act together to have their kids in the same classroom as troubled people. We can't make you do that, but we can tax your money and only give it back in the form of education with no competition."
I don't know if they're really saying that, but it really sounds that way to me. It's like they're afraid they can't sell the idea of taxing me to pay for the education for the poor, something I personally would support, so they have to sell it with the idea that it is for everyone and MUST be for everyone.