[marnett]

At least in the US the main reason is the public hysteria that would be brought on by the mass cultural shift. The reality is most households in the US do not have masks. There would be similar chaos that the US has seen with toilet paper but on a more dire scale because they DO actually help and, unlike toilet paper, when they are gone they WON'T be replenished in a timely manner because there is a shortage of retail masks.

It's propaganda. It is reasonable propaganda as having to have actual PSAs on how to sew your own masks or make them out of materials at home would really start ramping up the general anxiety.