Just as there are charismatic megafauna, there are charismatic mega-ideas. “Flatten the curve” could be one of them.
"Most of our philosophy, our epistemology, and our definition of science come from pictorial representations, not from an experience of vision or from an experience of actually seeing the world." (Latour 319) Things like pandas and graphs which represent ideas and goals could fall under Latour's "pictorial representations", which they argue drive most of our worldviews
there are charismatic mega-ideas. “Flatten the curve” could be one of them.
Robinson is drawing a comparison between the idea of "flattening the curve" and charismatic megafauna. People concerned with wildlife conservation use lovable animals like pandas, elephants, etc. as a "poster child" for their cause. It's just a given for many people that they should be protected, thus spurring action from people who may not be as interested in the nitty-gritty scientific details. I think the idea of flattening the curve definitely has a similar effect.
charismatic megafauna
"a term used to refer to the plant and animal species that have a large appeal, perhaps due to an attractive appearance, to a global audience ... generally associated with environmental activism and conservation messages" - WorldAtlas.com