The rise of Villians
Everyone knows that every story needs a conflict. What's better to create a conflict then with a hero and a villain. Even better superhero's and equally awesome supervillains. For all the goodness there must be some evil to counteract it and create friction.
Good and evil.
Rise of the likable villain.
Authors and film writers are trying to create more in depth and realistic characters. One way to do so is make an unlikable hero like Tony Stark, or, at times, Katness Everdeen, or Woody from toy story. The flip side of that is to make likable villains such as Darth Vader (even though he's been around for awhile), or Loki and Deadpool (though some would say he's the hero), the Joker and even Hannibal Lecter. This type of storytelling creates an intense twist on the entire good and evil balance. Which is always fun.
Good and Evil
It's also fun to push societies views on what is good and evil. Fictional stories tend to strive to define the two extremes yet most characters fall inside the gray area in between. People feel for the villains because their more realistic, more interesting, and more mysterious. While watching Thor, I felt like I learned more about Loki than about Thor. Which I kind find of funny. Of course people get more attached to what they know more about. Except for the joker, he's just ....different. So the rise of likable villains may be because people are redefining what is evil. People want real characters with understandable problems. Or the directors just find really good actors, whatever you wish to think.