You don't understand how massive psychological damage can be as bad as seriously endangering someone's physical health?
Just because a graphic description of a dog being raped while a child watches doesn't bother you doesn't mean it won't bother anyone else. In fact, I would wager that it would be pretty disturbing for most people to read that, let alone read that sort of thing for hours every day.
And then there are the ones who are just as low-paid but have to look at images instead. Again, you may not be bothered by CSAM, but I would wager that most people would find looking at that all the time very hard to deal with and it could easily result in PTSD.