It's just not necessary:

The gold standard for medical evidence is the randomised clinical trial, and the gold standard for analysing this evidence is Cochrane (formerly the Cochrane Collaboration), the world’s largest and most respected organisation for evaluating health interventions. Funded by the National Institutes of Health and other nations’ health agencies, it’s an international network of reviewers, based in London, that has partnerships with the WHO and Wikipedia. Medical journals have hailed it for being “the best single resource for methodologic research” and for being “recognised worldwide as the highest standard in evidence-based healthcare”.

It has published a new Cochrane review of the literature on masks, including trials during the COVID-19 pandemic in hospitals and in community settings. The 15 trials compared outcomes of wearing of surgical masks versus wearing no masks, and also versus N95 masks. The review, conducted by a dozen researchers from six countries, concludes that wearing any kind of face covering “probably makes little or no difference” in reducing the spread of respiratory illness.

"Approximately Zero": What the Best Evidence Shows Masks Do Against Covid – The Daily Sceptic

John Tierney has written an excellent article in City Journal summarising the latest Cochrane review showing masks do "approximately zero" against Covid. But the U.S. has no intention of following this science.

^{Will Jones (The Daily Sceptic)}