The success of SNAP comes despite its inherent inefficiency, friction, and the indignity of its limitations. We structure the program the way we do in order to mollify voters who twitch at the idea of the poor ever enjoying anything.
Inequality isn't just about healthcare costs, biological metrics, etc. It is also deeply corrosive socially and psychologically, and this side of things is systemically underappreciated in policy circles.
To be sure, our food and diets are bad. Americans broadly should eat healthier. But are society's interests really better served by insisting that a poor child not be allowed to have a cake and blow out the candles on his birthday, the way all of his friends do?