There have been a lot of ads for face masks since the recent coronavirus outbreak, but Facebook has decided these ads are doing more harm than good.
Facebook had already banned the making of medical claims of effectiveness about products, so no one could market their product as 100% effective in preventing the disease. Face masks are far from being 100% effective, and even the CDC has discouraged the general public from using them.
Facebook also expressed concerns about price-gouging. They are worried that sellers would take advantage of the panic in order to sell their products at hugely inflated prices.
Facebook is a hugely influential platform, so they have a lot of responsibility in their management of it. If they took a more hands-off approach, they might allow the panic to get worse than it already is.