Sometimes organizations do things certain ways because that's the way they've been done in the past. Organizations need to adapt to changing circumstances. The costs associated with illiteracy in general are extensive.
Discrepancies in per-student spending between public K-12 school districts in local areas are a significant driver of inequality and reduced upward mobility. Under-educated individuals are less likely to function well in society. Incarceration and criminal activities stemming, in part, from poor education cost society more than education.
Most of the funding for these schools comes from state and local sources. Funding between districts can vary widely due to differences of wealth between districts.

