Why “Just Add a Belt” Doesn’t Create a Waist (explaining the science behind this myth)

The H shape body guide is making sense to me. The one piece of advice I find confusing is to avoid anything at the waist. I though if you don't have much waist definition you can fool the eye by adding a belt or using contrasting colors where your waist should be (in my case, used to be.). Can you elaborate on why this doesn't work? I like to wear full length, high waisted pants with a jacket that hits right at the waist or a peplum top with a fairly flat bottom ruffle the same color as my pants ...