You searched poorly, PubMed was quite full of medium quality evidence for their use, back from 2008. Even against influenza which is notoriously widespread and

You searched poorly, PubMed was quite full of medium quality evidence for their use, back from 2008. Even against influenza which is notoriously widespread and harder to control. Evidence against was at most due to low adherence. Which means so much as masks don't work if you don't wear them, and they're annoying enough for general public. Quite obvious. Face shields are somewhat less tested, and likely much less effective based on theoretical data, as they don't form an effective barrier.