The whole point is that these companies are spending a lot of cash making sure that their products are as addicting as possible to as many people as possible, so "just" shutting the phone off isn't a viable strategy.

It's as idiotic a statement as saying "Just stop smoking" around the time when big tobacco was lobbying politicians and bribing scientists and doctors to straight up lie about the deleterious effects of tobacco. It's engineered in such a way as to make it basically impossible for a large swathe of the population to "just not use" the apps.