> How did there come to be schools that were predominantly black?

The residents in their area are mostly black.

> Why is school funding tied to property taxes?

That's how most of your city is funded.

> Why isn't there a level of mobility that would allow students to go to a more well funded school?

There is? Like, you can move to a different school district but it's going to be more expensive. Nobody is preventing you.

> Who made these policies and why?

It's not clear what policies you are referring to. That we fund things via property taxes?