A couple of reasons for this spring to mind immediately. Firstly, governments don't want people using the most effective masks because there's barely enough of

A couple of reasons for this spring to mind immediately. Firstly, governments don't want people using the most effective masks because there's barely enough of them to supply hospitals. Secondly, the push for masking has absolutely nothing to do with effectiveness. For instance, people keep pointing to things like the 1918 flu epidemic as proof we've always known masks worked, but as far as I can tell those masks were made of gauze and therefore likely as bad as or worse than the worst mask in the study. And there was an article going around pointing to this study of the effect of reducing the dose of flu virus people were exposed to as proof masks worked better than expected: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4342672/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4342672/ Notice how, at the part of the curve where reducing the amount of virus had the most effect, it took a tenfold reduction or so to reduce the number of people showing symptoms or testing positive by about 30%? On its face that seems kind of bad for the idea of using random non-medical face coverings with much worse filteration, but that's not how it's been spun. Also, I think a lot of this has to do with what people feel will work based on it having a good narrative attached. For example, there's this fairly widespread idea that valved masks are not OK and worse than random cotton face coverings which I think has even been enshrined as an actual legal requirement in a few places despite clearly not matching up with the test results here. Presumably this is because it feels like deliberately letting your own breath out past the filter via valves is intentionally exposing others, even though anyone who wears an ordinary non-fitted face mask can easily notice that exhalation blows out around the edge of the mask anyway - often with really annoying results for glasses wearers. A bunch of British news organisations even accused our government of telling people to wear "useless" maasks and endangering the public for showing a valved mask in their advice: https://www.independent.co.uk/news/uk/politics/coronavirus-face-coverings-masks-valve-downing-street-messaging-a9619436.html https://www.independent.co.uk/news/uk/politics/coronavirus-f...