I think the truth is we would not make another Fantastic Four movie until it was ready to be made.
The studio released two Fantastic Four movies during the 2000s to mixed results (in terms of both critical and commercial returns), before moving forward with a reboot some years later.
Despite having a great cast, including Toby Kebbell as the villain, studio interference and behind-the-scenes trouble with Trank ultimately sent the Fantastic Four reboot flying off the rails.
After establishing the X-Men universe in the early 2000s, 20th Century Fox hoped to add another superhero franchise to their core schedule.