Simply because there're different rules. In Rio in some public places fascist certificates are required, including some hotels, and I keep withnessing it myself. In Sao Paulo starting the Jan 10th, it's required in all public places, I've heard. And in Rio will be, in all the places, starting from the carnaval.
You as a foreigner can show me something which resembles a
certificate, and it'll do, but the rule is in place.
And in general, brazilians, mostly, wear muzzles religiosly. And wash hands with chemicals too, all the time. I never do, and sometimes I'll argue with them whenever I'm asked to wear a muzzle.
Today once I left a coffeeshop, it got closed, and when I came back, it was still closed and there was an explanation: "we are temporarily closed due to the growing cases in RJ. We don't know when we'll return". Higly vaccinated Brazil in its best.