Why do some people choose not to wear a mask?

They don't protect the person wearing them only other people and perhaps they couldn't care less about the other people.

Let me start by saying I'm a clinical nurse specialist who has been working on a Covid-19 ward for the past three months.

Initially, we had a pretty good idea that this virus spread primarily through contact. A person sheds these viral particles by coughing, sneezing, talking, singing, breathing, etc, liquid droplets containing the particles adhere to surfaces and can then be transferred between people. The droplets can also be transferred directly between people without the intermediate surface. The virus can be aerosolized and become airborne. We know that it can stay suspended in the air for periods of around 30 mins. Which means particle loads can build up in indoor, crowded areas.

The problem was that messaging on masks evolved as things progressed. Initially the public were told not to buy masks. The reason for that was simply because the priority was getting them to hospitals. The lockdowns started, and footfall in the few shops allowed to open (grocery stores, pharamacies, etc) dropped. In this scenario, masks weren't all that necessay because the risk could be effectively managed by handwashing and 2m / 6ft social distancing and the fact that people were isolating themselves and their families.

Now we are in a different situation. Businesses and offices are opening. Public transport systems are operating. More people are mingling indoors. At this point it makes sense that people should wear masks to reduce risk (and hence the WHO advice changed to reflect these new scenarios), but that is an additional measure on top of social distancing and handwashing and not a substitution.

And this is one of the issues with masks ... they are a nice, comforting, easily visible sign to other people that you are being socially responsible but it can start to become an issue of contention, anxiety, anger, etc. The reality is, provided people are maintaining their social distance and washing their hands, they too are doing their part to substantially reduce the spread of the virus. 

I've been isolated for months since my risks were high and only recently have been back into what I'd call normal-ish society. I watched people in my local supermarket. People had masks upside down. They had masks inside out. Some walked out of the shop, took the mask off and dumped it in the bin. They didn't wash their hands before or afterwards. People fiddled with their masks, adjusting them, fixing the strips over their nose, the ear straps, and so on. Some people had big gaps around their chin and neck. Some pulled the mask down to talk to people, then pulled it up again. I'd estimate that about 50% of the people wearing masks I saw would probably have reduced their risk by not wearing it!

This has always been the concern. If you make masks mandatory then it could be counterproductive. I'd advocate mask wearing but it has to be followed with an intensive information campaign.

One final issue to consider is that some people can't wear masks, such as some asthmatics. So it is deeply unfair to make masks mandatory and we shouldn't judge people based on whether they wear masks or not.

At this point it becomes a matter of personal responsibility. Where politicans have failed is in national campaigns to explain the issues around masks, provide information, and then let people make their individual choices.

So ... the reason people don't wear masks is because of lack of information, lack of social responsibility, and confused messaging on whether they needed to wear them!

It's the red neck males to prove (again) they have a dick. To show off their 'machismo'. It was the same in the 1980's with AIDS/ HIV the same sort of guys wouldn't wear condoms then either. They made everyone sick and killed millions. 

Now they are doing it again.

They don't protect the person wearing them only other people and perhaps they couldn't care less about the other people.

I think it is because western countries have been given bad advice on masks from the beginning.Eastern countries, specifically oriental countries, know that masks work, which is why they are mandatory in many places. Countries where masks are mandatory have about 1% of the number of cases in countries where masks a not worn. Also scientific studies show that masks keep everyone much safer. 

I wear a mask whenever I go out. People look at me, but I do not care. I would rather wear a mask now than a ventilator later. 

Because the devil is busy and when he is done with these selfish evil tools, he will own their souls to no return, they will suffer for all the lives they infected..but they know not. I can see if someone is lacking the mental capacity to understand but experts of medicine have told us what’s going on, how to protect ourselves and others and how this contagion spreads

Because coronavirus is greatly exaggerated.

There are too many conflicting opinions Michael , and from the supposed experts it is confusing its not a natural thing is associated with crime and fear uncomfortable and of course not flattering for the ladies , its no real excuse but thats the best i can do 

Because some people are stupid and selfish.