I didn't know that we're supposed to artificially introduce disappointment. I just let the kid get there itself, and she's not the worst at it.
The problem is that if they are spending most of their experience time online, what kind of disappointments are they getting, and how can a parent monitor and understand it, when they don't even talk?
I'd say that those parents who let their kids spend a lot of time online don't have much interest in parenting, in even wanting to understand, nor would they think about disappointment as an important part of life. So many parents just wing it, with no further thought. Here comes the loss of narrative into play, the loss of community where our behavior is influences by the stories of our grandparents and neighbors. These days, nobody cares about stories anymore.
I reckon this has largely been the case in history, with the difference being that in history society used to teach many of the skills parents would need. Now, people are conditioned to stay immature children, and then become parents.