Why can't we steal food from grocery stores that throw food away?

Every day, grocery stores throw away massive amounts of food that is expired but still safe to eat. I'm talking bread, veggies, juice, milk, fruit, bags of chips, etc. Someone told me I could get arrested and charged with a felony for shoplifting, even if I only steal food. It seems unfair to face criminal charges when grocery stores are just going to throw the food away anyway.