This also resonates with recent sentiment that telling people that "masks don't work" (with the intention of keeping people from buying masks when they are scarce even for health care workers) can backfire significantly:

https://www.nytimes.com/2020/03/17/opinion/coronavirus-face-...

The major reason why masks are not promoted on a wide scale is because there simply are not enough masks right now. Simple DIY masks are not perfect, but certainly better than the current state of hardly any use of masks in public at all.

Abstract: "We demonstrate that widespread use of masks by the general population could be an effective strategy for slowing down the spread of COVID-19. Since surgical masks might not become available in sufficient numbers quickly enough for general use and sufficient compliance with wearing surgical masks might not be possible everywhere, we argue that simple do-it-yourself designs or commercially available cloth masks could reduce the spread of infection at minimal costs to society."

And there are sites like Wirecutter that a lot of people hold in high regard and pushing the don't use mask message

https://thewirecutter.com/blog/face-mask-for-coronavirus/