It’s not that 20% of the people randomly wear masks. It’s that people with symptoms of a cold or flu wear them. As a social courtesy to try and not infect other people. I realize that there is a not insignificant number of people in the US who can’t imagine doing anything to slightly inconvenience themselves for the benefit of others so we’re not likely to see similar behavior here. Hell, we often don’t even see it here in the middle of a deadly pandemic.