All those kitchen goodies are the equivalent of giving kids all the popcorn and candy they can eat all day and then wondering why they aren't hungry at mealtime. You need to cut out the snacks and provide only the commercial food until they fatten up, because that's where the protein is that will enable them to put on lean muscle mass.
They need to learn to eat the protein and not the snacks, just like kids, you see. Once they put on some weight and look healthy you can add a LITTLE extra goodies.
@PirateGirl , think worms could be a factor?
Every single thing they eat is a factor. You can't stop them from eating plants and bugs and worms off the ground and only eat their feed. And none of the things they are finding naturally or that you are giving as snacks are unhealthy. It's just that they are likely not eating enough protein overall. The most protein is in their feed. Cut out the things you do have control over or get a higher protein feed.