It's not 'obvious'. The goal of that chart is not to be a perfect representation of history. It's to show 'greatest hits'. Foucault was a superstar-philosopher who was a regular TV guest. His panopticon analysis is way more widely know than Goffman's analysis (as much as I love Goffman).
Sure. But why this urge to rewrite history then? Just because Foucault is the grandfather or surveillance studies? Why forget all these older and more fruitful discourses?
