I think all the theories here are cool. Here's my two cents: desenitization.
See, we look for that kind of stuff all the time. I remember watching tons of gory stuff in my free time. It's the same reason tons of people here say the n word, they are desentitized to it. When you have a ton of something it is less exciting and more normal. It's a reflex from our ancient monkey brains to get us to like things from different enviornments, like how we like to eat different food from time to time. Different = good, same = okay
The same thing even happens with poison and pain. If you do something every day it becomes less effective, and allows you to build immunity.
I obviously am just theorizing here, but I think that's why.
