The evidence they had was of such low quality that no solid conclusions could be made from it. What they found in the research may not reflect reality. They are explicit about this and stress the need for better research.
> "There is uncertainty about the effects of face masks. The low to moderate certainty of evidence means our confidence in the effect estimate is limited, and that the true effect may be different from the observed estimate of the effect...There is a need for large, well‐designed RCTs addressing the effectiveness of many of these interventions in multiple settings and populations, as well as the impact of adherence on effectiveness, especially in those most at risk of ARIs."
They admit that they were unclear about it and later were even more explicit.
"Given the limitations in the primary evidence, the review is not able to address the question of whether mask-wearing itself reduces people's risk of contracting or spreading respiratory viruses."
The review is not able to "address the question" let alone conclude anything about the impact of mask wearing. The review is inconclusive.
> The evidence they had was of such low quality that no solid conclusions could be made from it.
OK, fine. If I grant this (I don't, but let's run with it...), it means the following is also true: we mandated something based on such low-quality evidence that no solid conclusions could be made from it.
> "There is uncertainty about the effects of face masks. The low to moderate certainty of evidence means our confidence in the effect estimate is limited, and that the true effect may be different from the observed estimate of the effect...There is a need for large, well‐designed RCTs addressing the effectiveness of many of these interventions in multiple settings and populations, as well as the impact of adherence on effectiveness, especially in those most at risk of ARIs."
They admit that they were unclear about it and later were even more explicit.
"Given the limitations in the primary evidence, the review is not able to address the question of whether mask-wearing itself reduces people's risk of contracting or spreading respiratory viruses."
The review is not able to "address the question" let alone conclude anything about the impact of mask wearing. The review is inconclusive.