These characters right here.
Marvel's first family.
A combination of no direction, a string of runs that didn't connect and their roles in the MU being supplanted by other characters.
Tony Stark has replaced Reed as the smartest and go-to guy in the Marvel Universe.
Sue Richards has always gotten the shaft when it came to relevance. Sadly, both her and Jean Grey haven't been given anything to do in decades.
Johnny is running with the Uncanny Inhumans now, but I don't think anyone ever connected with him the way people did/do with Peter Parker or other flash young heroes.
Time for a riddle. What has 20 legs and comes in assorted colors?
Answer that and you'll know why Ben Grimm doesn't matter anymore.
Hickman's FF was the last time in recent memory the FF really made a difference and had direction and before that, Byrne in the last 70s-mid 80s.