It's because they don't understand the effects until they happen. This of course doesn't mean they can't learn. Look at what happened with smoking and other harmful habits. We were bombarded with ads left and right, even taught in health class about the harmful effects of smoking and drinking. I remember them showing us a smokers lung and it was disgusting beyond words. However, not a single second was dedicated to hearing loss even though EVERYBODY carries an audio device with earphones.
All I heard was, "Don't listen to loud sounds." Okay. What is loud? I may have learned to avoid loud machinery in the shop but I'll go on listening to my earbuds, destroying my ears because I had the volume up 3 notches above safe levels. It is too damn easy to cause damage as evident from the growing number of cases. Even the little amount of literature that is throw our way is piss poor in terms of quality. I kept reading about a pure tone sound like EEEE. I never read about a static hiss that builds slowly over time. I was never warned that the sound can be easily ignored because of how subtle it is.