Fauci has widely explained why he felt it was justified at the time, admitted he was wrong, and apologized. Like when I just started to do a search to provide sources, it autocompleted the query even. Probably similar for the other sources you named, so I encourage you to do some research if interested.
No, the problem was that people took the statement that we didn't yet have the evidence on efficacy to mean that masks were useless.
Not having evidence... Means that things can go either way. And the WHO didn't even stop by saying no evidence, they said no evidence, and then went ahead and said it might help anyway.
> Although there is no evidence that this is effective in reducing transmission, there is mechanistic plausibility for the potential effectiveness of this measure. - WHO