That's a very good point. As I understood it, even if we ignore the people that don't cover their nose, you have to be very careful when putting one on, to get the desired protection. Most people just don't care enough about it. Also use them to often, yada yada yada...
Good advice and easy to do. Just use your favorite source to find review articles. You don't need to read many, as conclusions were quite uniform.
It was only after 2020 that any studies were done on effectiveness in use. The results are a lot more positive there. However, it was still difficult to do controlled studies so the results aren't as strong as one would like.
1. Epidemiological: "Town A mandated masks and town B didn't. Was there any difference in reported rate of pathogen spread?" Reviews over the past century of epidemic responses indicated no overall benefit.
2. Clinical: "In a controlled situation, was there a difference in rate of pathogen spread between the mask-user group and the non-mask group?" There was soft support for some benefit in non-sterile, close-contact environments.
3. Laboratory: "On a laboratory bench, what degree of pathogen capture was achieved by the mask apparatus?" These studies assume that performance on the bench correlates to performance in the field. The N95 mask is a case in point. On the bench, it performs better, but reviews of clinical studies didn't find a strong effect in field use.
That's how we got the pandemic.