Even though the image you show of Brazilians all wearing masks from the perspective of a telephoto lens, it does not show people using the 6 foot rule. That kind of crowding would be all it takes. However Brazil was lax in the needed mitigation efforts in the plague’s early phase of growth. A skeptical president with millions refusing to socially isolate themselves, caused the virus to take off.
so now it’s social isolation. You said masks prevent the spread of disease so you shouldn’t need social isolation.