Continuity mistake: Sue's hairstyle, as well as the texture and length of her hair, and the color, changes from scene to scene, and even at times from shot to shot. This was due to movie re-shoots.
Continuity mistake: Young Reed has blue/green eyes but older Reed has light brown eyes. Eyes never change color with age.
Continuity mistake: When Franklin sees Johnny on fire for very first time, he is lying on a pad, but in the next shots the pad is gone.
Chosen answer: In a nutshell, 20th Century Fox and the people that worked on the respective films simply don't understand the comics and why fans like the source material. It's also worth noting that the 2015 film was made so that Fox could retain the rights, as they would have gone back to Marvel had they not begun production on it by a certain date in 2014. They weren't exactly making the film with the intention of it being great, rather as a rights grab and a money grab, though the film ended up being a major box office flop, so the latter didn't exactly pan out in their favor. There are many fans that would like to see the rights to Fantastic 4 revert back to Marvel Studios, as they would more than likely do the films justice.
Phaneron ★