My theories...
People have been using HEPA vacuum bags to make masks. Since bagged machines of any variety are in the minority, this phenomenon may have caught suppliers/manufacturers by surprise because suddenly everyone needs vacuum bags when for several years now, the demand for bags have decreased as everything except for high-end are pretty much bagless. Did those long-lost bagged machines suddenly rise from the dead? Probably not.
You wouldn't believe it but a couple months ago our scheduler for the HVAC-R company I work for received a call asking if we had a large amount of HEPA filters (well, we do have HEPA, but they're typically reserved for higher-end, specialized and usually commercial installs designed to handle HEPA media as the air handlers of those systems HAVE to be optimized for HEPA, so they really meant MERVs which are very commonly mistakened as HEPA) as they wanted to create masks out of them. I'm not a medical professional, nor am I a tailor, but I don't think an HVAC filter would be the best option for a face mask.