Partly a self-reinforcing problem. Ignorant and stupid people don't value education. Providing less education means more people like that, which can lead to less education, and so on.

Capitalism benefits from a poor underclass to exploit their labor. Racism is a mechanism to keep labor fighting amongst itself. I recently read "Dying of Whiteness" and it was a fascinating, but depressing, look into it.

Racism, or more broadly antagonism towards the out group, can also harm public services like education.

If you have more specific questions I can try to answer, but it's not my area of expertise. Another "but why" won't get a response from me, here.