It's not optics, it logistics, science and psychology.
Costs? Just imagine how you would do it if you were in the government.
A mask on its own may be cheap but for a whole nation? They have to be manufactured, where from? They would have to be distributed, how? You'd need to send everyone at least 2 of them. That's over a hundred million of the things.
Okay, so lets imagine you were able to find a manufacturer of a hundred million cotton masks and were able to buy them, and were able to send them to every household in the country. What should you imagine next? Why should anyone wear them if they are not being serious now? What should you do as a government to get people to wear them? Shouldn't be against the law not to wear one? Who would enforce that? How much publicity would you spend, who would write the advice and how would you do broadcast it? Do the scientists agree with this? Wouldn't social distancing work just as well? Could people feel more safe wearing them and break social distancing? There are more questions you could put here with some imagination....
I feel we are panicking and reaching out for any stricter solution. I'm seeing many left wing people on social media in the UK call for stricter approaches, but that is partly to oppose the government whatever the cost and partly fear. How about the army on the streets enforcing curfew? That would be effective and probably quicker than cotton masks. How about mass surveillance? That's just digital and doesn't need anything manufactured, nor paying the army. We can easily and happily give up our rights and liberties when we are scared - after all we are saving lives and so many people are lacking seriousness.