Exactly, Marvel and DC have a whole back catalog of characters that they could "exploit". Not to Mention that Image/Wildstorm, Top Cow have ones that could do well, like The Darkness, Witchblade, The First, etc.
There are a bazillion characters, but how many of them are actually big money... Hell, Green Lantern should have been a monster at the box office... It was lack luster to say the least.
When you look at BIG MONEY characters, most of them have been done or are already in development.
No one wants to see Dr. Strange or Firestorm.
Look at how poorly the wonder woman reboot was received... And was I the only guy who watched Jonah Hex?
Let's just be real, I'd love to see a (Fawcett) Captain Marvel, but it won't happen... There is no market for it.