While I think that is an excellent idea in theory, keep in mind that if SNAP were to be teatricted to healthy foods, several other things would have to he taken into consideration.
For one thing, WIC is designed for the nutritianal needs of a pregnant woman and infants and children through age 5, and there are sometimes alternative options available upon proof from a doctor that the standard items available do not apply to a specific individual. For instance, an infant who needs special formula.
Another thing to consider is that many of the healthy alternatives to boxed foods, processed foods, snack foods, etc. are more expensive. Do families or individuals get an increase in allotted SNAP benefits to cover the editional expenses? Granted there are ways to minimize the expense, but that isn't always as easy as it may sound. Families living in motel rooms, for instance, without access to an oven. It's more common than one may think. I have seen it firsthand. Or homeless who can't always home cook their meals. Besides, who would decide what foods are considered healthy enough and which ones are not? Who decides how to meet the nutritional needs of various groups of people?