movies

Ratings aren't that important. The sequel did slightly better ratings wise.

The first film had a budget of ~$100 million, and made ~$330 million. That's a solid hit, maybe a little rough if the marketing has been super expensive.

The second film had a budget of ~$130 million, and made ~$300 million. A bit of a dip, but again unless they spent bonkers on marketing a decent return.

The problem is the films were early 2000's films coming out in the late 2000's. Up against the original X-Men, sure they're worse, but not God awful.

Fox had just put out X-Men 3 the year before and it was a mild success. Maybe in a world with no other superhero films Fantastic Four 3 would have been made. But that isn't what happened.

In 2008 we got The Dark Knight and Iron Man. Those films changed audience expectations of what a superhero film should be. Probably Dark Knight more than Iron Man at the time, but Iron Man set up the idea, it teased The Avengers.

Maybe it was too late. Maybe The Fantastic Four was already over. But importantly no one cared about The Fantastic Four at that point. Fox was not going to be able to pull together a third film to compete. X-Men was already the more popular franchise, so that's what they focused on.