I don't think it's a matter of shortsightedness. It's more a matter of the properties not really meshing well at all. What good does it do to have five or six superheroes in a world packed full of mutants? Or to mix cosmically powered superheroes with a street level hero like Daredevil? Fantastic Four, Daredevil, X-Men, not a single one of those franchises mixes with either of the other two, and combining them would make the the whole weaker than the sum of its parts, not greater. It's an altogether bad idea.
One thing I do think they should do, though, is put out more X-Men movies. An idea they should take from the comics is the idea of the X-Men Gold and Blue teams. They've got so many characters that they can easily put out two concurrent movie franchises side by side, and interconnected. X-Men Gold Team movies and X-Men Blue Team movies. There'd be a few tie-ins here and there in both sets of movies, like Professor X, but for the most part each series of movie would have its own cast of characters, plotlines, and villains.
The X-Men Blue Team, which we'll call the Astonishing X-Men movies, for one, could feature Cyclops as team leader and have the Marauders, Mr. Sinister, and Apocalypse as the villains. Meanwhile the X-Men Gold Team, which we'll call the Uncanny X-Men movies, will be led by Storm and feature Arcade, Bolivar Trask, and the Sentinels as the villains.
So while should absolutely NOT mix the X-Men, Fantastic Four, and Daredevil together, they can certainly expand the X-Men universe a bit, and to pretty good effect.