(1) Many poor school districts are urban (2) Many urban dwellers are not owners, they are renters (3) Schools are funded by property taxes payed by owners (4) Often, the owners are large corporations, that do not involve themselves in anything about how the schools are run.

Basically, poor, urban schools are largely funded by faceless corporations holding hundreds of apartments paying taxes, not random rich families with luxury condos in the city sending kids to private school.