Charter schools are wonderful, if the state's laws are well written. I'm in Minnesota, and my kids went to charters for seven years, (six at a project-oriented school that targeted students with learning or social problems in mainstream schools). But it works here because the system is completely fair - any student can attend any school, and there are no good mechanisms for private charters, or for charters that exclude students by type. Many of the charters are actually sponsored by school districts - for example, Minneapolis has dedicated bilingual charters for the large Somali and Spanish-speaking populations.

Then I see the consequences of bad law in other states, and I just cringe.

What prevents non-charter/magnet schools from doing such things?

Regular public schools are limited to the curriculum prescribed by their school boards and generally can't deviate or experiment much. They're also, by definition, limited to students in a specific geographical area rather than any selection criteria. As others have noted, this goes both ways - charter/magnet schools can choose to serve the highest aptitude students (as most do), but they can also choose to serve at-risk or academically challenged students as this one does.

So why can’t school boards prescribe such things? The geo limit doesn’t matter much/at all.

No explicit reason, they just generally don't. When you're beholden to voters or a city council, your job is least threatened when you don't rock the boat. If you do rock it, you better make sure you're right or it's not likely to end well for you. Meanwhile, your 'subjects' are unwitting participants who thought they'd be getting a normal education, not early adopters explicitly willing to try something new. All of these factors discourage experimentation.

Non-charter/magnet publicly funded schools cannot select/reject children based on their demographics or aptitude. The most they can do is have a preference based on locality or the presence of a sibling in the school - which can and does introduce its own selection bias.

Ultimately, the public school system has to serve students who have been excluded from more selective schools, otherwise you end up as a society where the most basic education is a privilege instead of a right.

I don’t see how that prevents them from improving education.

If you can select students who come from more better environments (magnet/charter schools), you don't need to spend a considerable amount of resources to manage/treat the social issues that accompany students from worse environments. The latter is what public schools that serve poorer communities have to deal with.

No, charter schools are a way to fuck over the 99% and ignore it while praising the 1%.

Unless you're using an unorthodox definition of 1% (e.g. 1% of demonstrated academic ability), you're mistaken. Rich people can afford to send their kids to private schools or live in economically segregated areas with high-performing schools. Charter schools do not charge tuition, making them available to the masses.

However, they often do exclude those who don't have parents actively demanding more for their children, those who perform poorly on standardized tests due to adverse home factors rather than innate ability, or those with special needs such schools aren't equipped to support.