You can't just put a commercial on TV and expect a bunch of people to show up and see it at the movie theatres. They have too many choices. They can just stay home and surf porn on the internet. Why would you want to go see The Avengers when you can watch like three people having sex from the privacy of your own home? You're competing for attention, and in a world where you're competing for attention, you have to figure out ways to make it more interesting for the audience to come out. It's no longer enough to be like "here's the movie, come see it".