Here are just some of the incentives overweight people have to lose weight:
They'll look better, to themselves and others. They'll have more clothing options. They'll feel better. They'll be healthier. They'll have drastically lower odds of many future heath problems. They'll live longer which means they can spend more time being with their loved ones.
Those are all incentives. Everyone who is obese has those incentives, even though different individuals may assign different values to them. Even with all those incentives that hasn't stopped the obesity problem. incentives don't incite action, but they can encourage them.
incentive noun [ C or U ] Something that encourages a person to do something by offering them a reward (https://dictionary.cambridge.org/dictionary/english/incentiv...)
You can have a ton of encouragement, but that doesn't mean it will be enough to incite a behavior. What definition of incentive are you using?
It literally says incite "to determination or action". Given that parents aren't actually taking smart phones away, neither determination nor action are present.
I'll grant you the examples you give incite people to desire to change weight just as negative consequences incite parents to desire that "something should be done," but it doesn't incite them to actually do something.
Describing something as incentive because it incites desire without changing behavior is not exactly what I think of when I think of incentives.
Think of being in the position of trying to come up with incentives for a group of people. Would you call your incentives successful if they created a desire in that group without anyone actually doing anything differently?
If I were going to try to come up with incentives for a group of people, I wouldn't try to create a desire in them. I'd try to give them something they already desired as a reward for doing what I wanted them to do. They'll probably never want to do the thing I want them to do. They might hate doing it. If the incentive is high enough though they just might do it anyway. If my incentives weren't enough to sway them, they'd still be incentives, just ones that were inadequate/ineffective. I wouldn't even be surprised if they failed. Incentives fail to cause changes in behavior all the time.