Single family detached homes require wealth, and are an easy way to discriminate between those with well heeled families and those without. This results in school districts where children in the well heeled suburbs have greater chances of “success” than those in urban neighborhoods.

Even if one doesn’t desire the actual quality of life of less dense areas, they rarely want to sacrifice the chances of their children’s future. See what is happening with NYC public education currently. Hence, the zoning requirements against high density housing is to keep certain socioeconomic classes of people out, especially as it would allow their children into the school system.