Even with your cynicism — and from your argument, why send them to school at all? — food is so cheap that paying for everyone’s school meals (even if they could afford it without help or hate learning) is a really cheap way to help those that are interested but can’t afford to eat well.

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).