There's an AP article out about the difficulties of changing snap. The enabling legislation defines food as anything for human sustenance, so to do otherwise will require Congress to amend the last legislation from 2008, which would require a functioning Congress. The other problem is defining what is unhealthy. It's hard to write a definition of that word that doesn't let a lot of junk food slip through.
If I were emperor, I'd say everyone eats for free. But the food is rice and beans, peanut butter, stuff no one wants unless they are truly hungry.