>>130124189They don't easily fit into the big grand epic blockbuster event format that superhero movies demand. The only story they have that's erally like that is the coming of Galactus, and you need to have established them already before getting into that. Likewise, even though an episodic format would suit them well they're too high budget for a TV show. They exist in a delicate balance between high profile events and low key stories, which doesn't translate very well to multi-million dollar filmmaking
I think the biggest problem though is just that the general audience thinks that the FF is just kinda dumb. They're not particularly edgy, their powers are seen as goofy (particularly Mr Fantastic's, who just looks weird in live-action), and ditto for the majority of their villains outside of Doom, Namor, and Galactus. Going gritty won't help them either, as Fant4stic shows. And speaking of, the bad track record of their past films doesn't help their public perception either.
