Let me use UK costs as an example, to show how cheap school lunches are compared to all the other aspects of education, because I don’t know the USA well enough: If I assume £2/school lunch (mine were £1, but that was the 90s), and if the school year is still 39 weeks, that’s £390/year, or £11,700 per year for a class of 30, compared to a qualified teacher’s starting salary of £25,714 (head teachers go up to £125,098 in London), and then you need to add the cost of books, and consumables, and the building itself, and insurance, and support staff (HR, caretakers, supply teachers).
Because the state requires them to be there anyway, so it's the state's responsibility to ensure they are well fed? Academic performance has no bearing on whether somebody deserves food.
Edit: we prioritize feeding people over giving them educational science articles; seems appropriate
All of this gets ignored because the poors deserve it or some stupid nonsense thrown around by the people with money and power
What other people are doing that is wrong is rarely particularly useful to think about when working toward a goal of your own.