That's exactly what goes through your mind as you watch Leviathan (this is the 2012 documentary, not the movie that came out later of the same name).
When my total-roof tear-off was done around 8 years ago those Mexicans didn't wear any harnesses. They looked as unconcerned as squirrels, they were used to it. AFAIK, none of them fell, it was a big crew, just one of around 6 (I think) working for a local roofing company. I've been up on my roof a zillion times, I'm used to it. If you're not used to it, it's very scary, but you can gain confidence, you adopt practices, hand-holds. But doing roof work is another matter, you get tired, there's debris, there's a ton of work to do, you have other guys around you, there can be the additional stress of hot tar fumes, the weather can be very challenging... hot, cold, wet, windy. It's tough work, dangerous.
Most of those jobs are based on making money in a short amount of time through contracts. When you're work is physical and you race against the clock with no oversight, union, etc. there will be injuries. I worked construction on and off for around 10 years and I only had one job where they enforced safety equipment and that was only after another company bought them out.
