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.

The countries you cite are all relatively homogenous. The U.S. has greater disparities in education funding due to funding coming primarily from local sources rather than national.

Sweden and Germany are no longer homogeneous at all, and anyway isn't diversity supposed to be a strength?

The specific example I gave, DC, simply destroys the argument that local funding is the problem. DC is very well-funded from national sources, and it has horrific schools.