Funding models differ greatly. Often those sky-high prices-per-student are because the schools are taking care of several meals a day for students, as well as before/after care, extracurriculars, and special needs programs, where all these initiatives are a necessity but unable to be provided by parents. In America, all of these are provided at higher cost and higher quality by wealthier parents themselves; in other countries, more robust social safety nets, more lenient workplace and parental leave policy, and occasionally higher real income/wealth per family allow parents to take on those needs at lower cost.
When combined with the prevalence of social intervention in the lives of poor families - up to and including removal of the children - you see that there is a profound and toxic distrust of these parents and of their ability to take care of their own children. We've allowed a model to grow where, instead of ensuring people make enough to take care of their families, we shift the burden onto the state. This is inefficient in education for a number of reasons, least of which the central conceit as described above, which undermines the effort at its core.