Why do parents blame...?

Because it's easier than blaming themselves for feeding their kids crap. Not saying it's right, but that's the general thought process. Really, the parents have all the control in the world. They could make their kids a nutritious, filling lunch. It's laziness at its finest. A cheeseburger is fine every once in a while, but if parents are depending on it as a typical meal for their kids, it shouldn't be a surprise that their kids are overweight. Simple as that.