Comment by blargey

The core message of "everybody will not just" is that you need to think about why people haven't already just, and address that.

With tooth-brushing and hand-washing people actually didn't know it was that good for you. So massive public health education campaigns about how they prevent acute illnesses turned out to be enough to get significant adherence. That both are very low-cost / low-burden / low-effort activities are also reasons that education on the benefits was enough.

(And educating the next generation of children to instill proper tooth-brushing and hand-washing as habits remains a perpetual ongoing effort; kids do not "just" either, they need to be educated the same way.)

Compare this to many "why won't everyone just" issues where the information is already out - merely re-proclaiming stuff already known by the audience that-will-not-just, and expecting that to turn the needle, is nonsensical.