I'm just going to say people, human nature, greed, and ignorance. Power lines when left alone aren't dangerous. However when we decide to get too close to them out of greed...
Just like a couple of years ago I took down a DEAD maple tree that I had no business going up in. I didn't do it for the money, but instead because a friend at the time wouldn't wait for the power company to come do it, and I wanted to help.
A cherry tree a few years ago that I chickened out of... somebody else did it, sucessfully... but out of greed or ignorance.
Then there's always the stupidity of those around you who can either get themselves, or you SEVERELY hurt or killed. The scar above my right eye is proof of that.