1) Originally the law exists so if you cut your finger you won't go to jail for "stealing" a bandaid from the first aid cabinet or other weird trivialities. I had a bad reaction to some taco bell and "stole" an entire roll of toilet paper in the bathroom by flushing it. For unusual situations not as a way of life to eat three meals a day.
2) Another intent is very short term survival. So if you are about to collapse in a low blood sugar diabetic coma, if you realize it and immediately slam a corn syrup soda, even if you can't pay for the soda its not a crime, because the overall cost to society of a collapsed or dead person in the aisle enormously exceeds the cost of a mere can of soda. But this dude paid for some needed food and snuck out with more food for later in his pocket. If his defense was he was feeling faint and ate it right there in the aisle as a sudden unpredictable (LOL) medical need, and said he was sorry but no wallet, that would be a realistic application of the law, but filling one's pockets for later use is pretty slippery slope.
3) The financial impact of the trial exceeds the cost of the crime by many magnitudes, and all the cost comes from the taxpayer. Thats fine when its something obscure like "policeman takes bicycle to chase down a criminal" or "earthquake hits store and customer steals bandages to save lives until the EMTs arrive". I stole a hundredth of a penny of water from the public water fountain because I was thirsty. However the financial impact of having to feed every homeless person is going to be a bit high and it makes no sense not to prosecute a common crime like food theft.
4) Proportionate punishment is an issue. So for me jail would be a ridiculous punishment for a couple pieces of food, but for a homeless dude, its like an all inclusive vacation.
Edited to add 5
5) Police punishment as non-judicial punishment. Sure the judge won't convict, but stealing a pack of chips means the cops will throw you in jail for a couple days. Much like political protesting is not illegal and you won't get a conviction for it, but the cops WILL let you cool your heels in jail for hours/days. Likewise maybe the appropriate legal level of punishment for stealing a cookie is sitting in jail and explaining yourself to a judge who lets you walk. Its not a crime you can be convicted of, but its not exactly government encouraged either. This is a likely outcome of the whole situation. There are parts of the country that "enforce" marijuana laws in a similar manner, or at least there used to be.
I mean that's a lovely headline and all, but in startups lingo, it doesn't scale.