Where have all the superheroes gone? Marvel, Disney, Warner Brothers, and the Weinstein Company are all snubbing this year's Comic-Con, the massive annual San Diego festival that traditionally previews and teases the most anticipated sci-fi, superhero, and action-adventure films. That means that the more than 125,000 fans at this year's convention, which starts July 21, won't be treated to early looks at the new Batman and Superman films, or the hotly anticipated John Carter and Real Steel. The Comic-Con buzz used to be indispensable for such films. So why are so many studios sitting out Comic-Con this year? Here, six theories:

1. Studios are saving films for their own fests

Two years ago, Disney launched D23 Expo, aimed at uniting its fans and building enthusiasm for its projects in the same way Comic-Con does. It's no surprise, then, that the studio is saving its upcoming sci-fi epic John Carter and the superhero extravaganza The Avengers, which it is distributing, for its own convention. Using those films as the expo's centerpiece would do wonders to boost D23's status as a "Disney-dedicated rival convention," says Geoff Boucher at the Los Angeles Times.

2. The films aren't ready

Marvel's appearance at last year's Comic-Con with the starry cast of The Avengers was the convention's "thunderclap moment," says Boucher. Now that the film is actually in production, fans were hoping for a more substantial tease this year. But according to some insiders, Disney and Marvel don't have anything to show that could compete with their "own past and wild fan expectations." Same goes for Warner Brothers, which isn't promoting its upcoming Batman and Superman films this year either. The films just "aren't ready to show much yet," says Deadline.

3. There's no room at the inn

Comic-Con may have gotten too popular for its own good. Studios and their stars are being turned away from hotels because they're overbooked, says B. Alan Orange at Movieweb. Fans were quick to reserve rooms, while studios simply waited too long to book. "There seems to be no favoritism involved, which means the obese juice chuggler from Minnesota may be the only Captain America you'll be seeing in San Diego this summer."

4. The nerds will see the movies anyway

"Comic-Con is a great place to generate buzz among die-hard fans," says Charlie Jane Anders at io9, "exactly the people who will go see a film on opening night, no matter what." That doesn't always translate into mainstream success. Scott Pilgrim, Sucker Punch, and Tron: Legacy were "sensations" at the festival, but fan excitement didn't turn into mainstream enthusiasm, and the films, by and large, bombed at the box office.

5. Negative Comic-Con buzz can doom a film

A negative reaction from Comic-Con can be instantly damning for a project. "The swarm of dedicated fans," says Brooke Barnes at The New York Times, "can instantly sour on a film if it doesn’t like what it sees." Publicity teams are then left doing an overwhelming amount of damage control. For some films, the risk just isn't worth it.

6. The festival is becoming more of a TV showcase

More and more big movies may be skipping the convention, but Comic-Con is becoming increasingly popular with genre television shows. True Blood and The Vampire Diaries have had wildly successful panels there, and, this year, some of TV's most buzzed-about series, like HBO's Game of Thrones, are proving to be the festival's big draws, says Anders at io9.