I wear a respirator almost every day at my job retrofitting homes to make them more energy efficient, which involves working in extremely hot attics working with fiberglass, as well as time in crawlspaces with exposure to mold, etc. The respirators are not comfortable by any means, and much of the time I wear a full-face respirator for eye protection, and those are even worse(I often have to literally pour the sweat out of them).
I mention this because as uncomfortable as respirators are, I think having lung cancer, reduced mobility, and needing to carry an oxygen tank around are much worse. And these guys at least have the benefit of a cool underground environment to work in. I think it's ridiculous that none of them wear there respirators even part of the time. I can understand taking the respirator off sometimes, even I do that. But wearing a respirator even half of the time would make a huge difference in their health, and is not as bad as they make them seem. I suspect peer pressure is a big factor, and that new miners are made fun of if they wear their respirator, or maybe they just don't want to be the only one.
There are also options other than simple respirators which are more comfortable. If I worked as a miner I would probably spend a few hundred dollars and buy a Powered Air pressure respirator(PAPR), which has a battery powered fan worn on a belt that blows air through filters, and sends it through a hose to the mask so that the user does not have to do any work to filter the air and prevents the feeling mentioned in the video of 'not getting enough air'. At 60K a year those workers can easily afford it even if they have to buy it themselves, and it's nothing compared to the inevitable medical bills. If any miners or freinds/family of miners are reading this, I strongly encourage you to look into this technology, I know that North Safety makes quality products.