The pouches are good for kids lunches. They’re disposable, so no cleaning required (yes, I agree that’s bad, but we’re lazy), and they theoretically have some nutritional value. I’m not saying this is good, I’m saying why people use them.
Similarly, they’re snack size. So when your kid says they’re hungry at home, it’s easy to tell the kid “get a pouch” instead of pouring some amount from a jar. Again, I’m not saying this is good, but it’s why they’re popular.