Well, here's the problem: the rights are all divvied up across multiple studios.
Marvel/Disney owns the Marvel Cinematic Universe, that's Iron Man, all the Avengers, SHELD, Daredevil etc. They're the ones who REALLY made that interconnectivity work, the characters can pop up from movie to movie and build up a story that continues, and other studios want in on that fat cash.
20th Century Fox owns X-Men and Fantastic Four, and those flicks are sort of winding up (Apocalypse will be the last one before the reboot). Those don't come out every year. I don't know if there's EVER been a good Fantastic Four (except for The Incredibles), I haven't heard much fan anticipation for it, but clearly the studio is hoping for big success. We'll see.
Marvel Comics literally cancelled the Fantastic Four comics in the new reboot, all the characters got resorted into other properties. the Thing joined Guardians Of The Galaxy, I think. That's the benefit of the comics and the MCU, they can move characters and actors around.
Columbia owns Spider-Man. Just Spider-Man, which is why the rebooted franchise was so dense with extra stuff, they were trying to build their own mini EU with all the villains (the Sinister Six). If they sit on Spider-Man long enough, the rights will revert, which is why they did the reboot in the first place. But the sequels make less and less money each go-around, which is probably why they worked out a sharing deal with Marvel. Columbia isn't going to fully give up the rights, and Marvel would be fools to give away the rights to their current and very-popular Miles Morales and Spider-Gwen characters, which the
**** fans would rather see. I don't think audiences are particularly interested in any more Spider-Man flicks.
Since DC is owned fully by WB, Warner is making all those movies: Superman, Batman, Wonder Woman, Green Lantern Corps, etc. This worked GREAT for them on TV because they had a pipeline going, but they don't seem to have that in movies like Marvel does. They do seem to be building up momentum, finally, after the horrible Man Of Steel, Batman V Superman and Suicide Squad look... interesting. But I can't imagine parents taking their kids to Suicide Squad, and Batman V Superman looks dark enough for some parents to say "I don't think so." MCU movies are far more inclusive, which means more tickets sold.
Universal is the only company that doesn't do superheroes. They're also the biggest earning movie studio, and have been for 15 years. So they have NO need to get into the game. But they still do big movies; Fast 7, Jurassic World, etc.
But a huge thing is that movies have to be events now, they need to be big and important enough to get people out of the house and into the cinema. They don't even have to be big, they have to be an event. Dramas, original stories, and so on don't feel important, so that's left to TV, who are happy to pick up the slack. Anything new or interesting in terms of movies will probably come from VOD services like Netflix or Amazon.
And it's worth pointing out that all these comics are OLD. Old old old. It's near impossible to conceive a genuinely new, interesting hero (there was almost a superhero arms race in the 60s, every superhero that could be was, only the strong survived and those are the ones we know today), and just as tough to launch one. So as audience interest wanes, we could see the rights for Spider-Man, X-Men and Fantastic Four lapse back to MCU/Disney, then we'll have a two-sided thing and there will be more spacing between titles and things might die down a bit. Maybe.