>People fear that delaying gratification will waste time, but in most cases its the opposite.

Yeah, this fear could be a big part of it. FOMO in general is likely a key point. 

>Many parents discount the value of healthy food for children. 

If I eat a lot of sugar, I can feel that my body becomes sluggish after a short period and my thinking far worse. What happens when that is the norm from near birth? I assume that "we are what we eat" and feeding the body well aids in the formative development of who we are to become - there is not much in our genes we can control, but we can set a better baseline for our physiology.