

This drop-off tracks with the brand. I say this as someone who likes the F4, they just don’t have a broad appeal with general audiences that other comic brands have. They’re a property that only comic nerds care about and always have been.
Edit: They also had to complete with Superman. The F4 have never been able to compete with Superman.
Future Foundation is pretty much the definitive modern F4 story. Hickmens run as a whole is peak.
A problem with the F4 is that their golden age of stories was back in the Silver Age of Comic Books. They were a cornerstone a lot of the early world-building of the Marvel Universe. Their lasting legacy has been the characters and ideas these stories introduced to the Marvel universe: Dr Doom, Galactus, The Silver Surfer, Black Panther, The Negative Zone, ect. Marvel has long struggled to adapt the team to the modern era.
I haven’t seen the movie yet, but IMO the best F4 stories are ones where they aren’t so much a team of super heroes, but rather a team of scientist and explorers with super powers. They are better suited to telling sci-fi stories rather then traditional superhero stories.