That would be fine during the early days of the pandemic, but it's been 1.5+ years already, people have had plenty of time to get/make masks. Most people should have at least one by now.
I'm more or less speaking of businesses that have reinstated mask mandates if they were previously lifted, or to a lesser extent, businesses that have mandates where no mask ordinances exist on a local level. However, I do agree that people should already have them on their own accord after 18+ months.