I've also found the actual epidemiological evidence for mask wearing being effective at preventing transmission lacking, despite the historical precedent and obvious mechanism of action.
I still think it's highly likely that mask wearing is effective (even the shitty cloth masks with designer brands printed on them, and in a sense beyond it being a good idea to as a cheap precautionary measure), but the lack of convincing evidence of that is surprising.
Please do keep in mind the time it takes to gather the data needed and then to write, peer review, and publish a rigorous epidemiological study.
You'd be very hard pressed to meet that standard in less than 9 months. Which means the first solid epidemiological evidence would not be available until, if we say that the epidemic went global in Feb 2020, until Nov 2020. And guess what, there it is!
I still think it's highly likely that mask wearing is effective (even the shitty cloth masks with designer brands printed on them, and in a sense beyond it being a good idea to as a cheap precautionary measure), but the lack of convincing evidence of that is surprising.