People like to push the envelope, especially filmmakers and TV producers. These days, darker subjects sell whether it is suspense horror or gruesome scenes.
Filmmakers will continue pushing the envelope until they cross the line that makes viewers not want to watch. Of course, even when they find that line, they know all they have to do is to stay as close to the line as possible until the audience is ready to cross it, then it will be pushed a bit further.
Of course, that is just for the dark films. Remember that they also make kid-friendly fare all the time. Although there is one thing I have noticed. At day care centers where I have worked, we are only allowed to watch Rated G fare. Very few theatre movies today are made for the G crowd. PG is the new G.
Last summer, I suggested "Lion, Witch and the Wardrobe" for a movie day. The director said that while it would be great, it as rated PG and thus, not allowed. Meanwhile, in college while observing in a state-sponsiored preschool, they allowed the 3-and 4-year old classes to watch "Batman Returns". Go figure.
MrBob