Long story short: Marvel Comics has cancelled Fantastic Four and removed them from merchandise said to be because of Marvel's Ike Perlmutter feuding over the film rights to the characters.
Newsarama posted a good article with quotes from former FF writer Jonathan Hickman which confirm why the series was cancelled along with comments from other industries veterans, which also debunk what Tom Brevoort had to say.
It should probably be worth mentioning that movies don't affect comic book sales and vice versa.
Marvel Comics editor Tom Brevoort on Fantastic Four back in 2016:
“Fantastic Four is a title and a concept that has a lot of built in historical importance in the Marvel Universe, but to the readership of today, it doesn’t resonate the same way that X-Men, or Avengers, or even Guardians of the Galaxy does right now,”
Former Fantastic Four writer Jonathan Hickman:
”I think it’s pretty common knowledge at this point that Marvel isn’t publishing Fantastic Four because of their disagreement with Fox,” Hickman explained. “While it bums me out, I completely understand because, well, it isn’t like they’re not acting out of cause. Fox needs to do a better job there.”
"‘Family,’ ‘Future,’ and ‘Exploration,’ are timeless, universal concepts. Sure, they can be nostalgic, but they don't have to be. That's really the brilliance of a lot of the early Marvel characters, they were created by guys wrapping both arms around timeless themes,” Hickman continued. “There are some exceptions to this, of course, but for the most part almost everything Marvel owns is highly malleable and easily exploitable. I'd argue execution is the mission critical element necessary for a Marvel book to succeed. Fantastic Four is no different.”
Kwanza Osajyefo, former DC Comics editor:
”Don’t tell me a talking tree and anthropomorphic raccoon can sell but the Fantastic Four can’t.”
Former Marvel Editor John Barber:
So I think it can connect with the audience - you just need the right story, and the right hook to draw people in to find out it’s the right story.”