A question that probably has plagued everyone at some point, I mean here in DC there are hundreds/thousands of different characters that people who haven't read comics, or looked them up, or whatever and....filmmakers just want to stick with Superman/Batman? YES we get it, these two guys are the biggest icons of DC...but they don't make up DC entirely if it was just them two the universe would be really...really...REALLY boring. Now folks lets take a look at all the movies that these two superheroes have had shall we? 
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Superman 
 
1. Superman 
 
2. Superman 2 
 
3. Superman 3 
 
4. Superman 4: Quest for peace 
 
5. Superman Returns 
 
6. Man of steel 
 
Batman
   
1. Batman(1966) 
 
2. Batman(1989) 
 
3. Batman Returns 
  
 4. Batman & Robin 
 
5. Batman Forever 
 
6. Batman Begins 
 
7. The Dark Knight 
 
8. The Dark Knight Rises 
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I'd rather not count the animated movies, because that'll just make the two lists even longer. So we got 6 Superman movies and 8 Batman movies(minus the animated ones, in which there would be 13 Superman movies, and 19 Batman movies).  

Now yes there are some other movies out there, but...compared to the Superman/Batman movies they might as well be dust in the wind. Now some will say the filmmakers wanna go with heroes that people will recognize......before Superman/Batman came on screen nobody knew who they were so why would it be so hard to introduce a new superhero now? 
 
At least with Marvel they have been expanding more on their heroes, showing Hulk, Ironman, Thor, Capt America, X-men and all them. But for DC the only heroes that they have shoved in the faces of the audience is Superman/Batman, now yes they did try something new finally with Green Lantern but thats just 1 movie...they can't just stop at 1 movie they need to keep showing the heroes not just giving them a single movie and being done with it. Filmmakers....you guys have so many heroes to choose from, to play with, to make great movies yet your limiting yourselves to only two of them. Here are a list of characters, in which there could be great movies if done correctly with the right script writing, actors, and settings. 
 
1. Flash- I am actually surprised this one hasn't been done already, its been in production since what? Ever? 
 
2. Wonder Woman- While not a huge fan of her, she does deserve her own movie at some point in time.
 
3. Green Lantern- You guys already made a movie, so why not another? 
 
4. Aquaman- Really needs it, and the film needs to prove that he can be a fantastic hero. 
 
5. The Question(Vic)- Theres plenty of conspiracies out in the real world, could be interesting to see on screen and Vic solving them. 
 
6. Martin Manhunter- Now...this one could be a little tricky, but could still work if done right.  
 
7. Hercules- This one could be a little strange, however Marvel put Thor as a superhero so why not Hercules?
 
Theres more, but am kinda tired to think of any other heroes at this point in time. So already I named 7 DC heroes, that filmmakers could use and make great movies in using them and thats not even scratching the surface of how many heroes they could put on the big screen. 
 
Alright sure, you can't do every single one but...eventually everyone is gonna get sick and bored of seeing Superman/Batman everywhere all the time. Just because they are two big popular characters, doesn't mean people can't get sick of seeing them everywhere they go. 
 
Anyway, done with this so agree or disagree doesn't really matter to me. Just wanted to give my points, on that there are so many different heroes filmmakers could choose from DC and expose them to the audience for those who don't read comics, or haven't gotten interested in DC and looked around to see what different heroes there are.