Despite Marvel's blockbuster success with its interconnected films and Warner Bros.' plans for the Man of Steel sequel -- featuring at least Superman, Batman, Wonder Woman and Cyborg -- and Justice League, Fox seems determined to keep its superhero franchises in separate universes, despite the occasional rumor to the contrary. But why?

"Well, it’s complicated," Simon Kinberg, writer/producer of X-Men: Days of Future Past and The Fantastic Four, tells Screen Crush. "Because none of the X-Men movies have acknowledged the notion of a sort of superhero team — the Fantastic Four. And the Fantastic Four acquire powers, so for them to live in a world where mutants are prevalent is kind of complicated, because you’re like, 'Oh, you’re just a mutant.' Like, 'What’s so fantastic about you?' [...] 'So, I guess we’ll go to school now. We’ll go to Xavier’s school.' No, it is, they live in discrete universes."

While that explanation will undoubtedly disappoint, and annoy, those fans hoping to see a comic book-style team-up to confront a global threat like, say, Galactus, it certainly makes sense: After all, comics writers have the luxury of largely ignoring the rest of the heroes and events of the Marvel Universe -- at least until it's time for the perennial summer crossover -- so why should Kinberg and director Josh Trank be expected to relaunch the Fantastic Four in the shadow of the X-Men?

X-Men: Days of Future Past opens May 23, followed by The Fantastic Four on June 19, 2015.