Jean's problem is Morrison and Bendis, together with a lot of the writers between them have basically trained readers to dislike her. Morrison pushed the idea that all she does is become Phoenix again, or the love triangle with Logan, and dying was the only important thing she ever did, Whedon and the other writers who followed him pushed the idea that Scott/Jean was a bad relationship, with constant arguments we'd never been shown, just so they could push Scott/Emma as better. Jean was popular enough for regular teases of her return, but they wouldn't actually bring her back, for the same reason Storm, Rogue and Psylocke were rarely in the main X-Men book anymore, everyone just wanted to push Emma instead.
Then Bendis wrote a time-displaced teen Jean and made her an brat that abuses her powers even before the infamous Iceman scene. By the time Marvel actually brought Jean back for real, how Bendis wrote her was influencing how people wrote adult Jean. More fans want Scott/Emma than Scott/Jean, but the same fans will reeeeee if Jean is with anyone else.
In addition to all of this, X-Men fandom still has a loud segment of older fans from the 1980s who can't accept Jean coming back after the Dark Phoenix Saga and have spent 35 years complaining about it as the moment that ruined their lives.
Jean really needs to be a central figure in a book with no Cyclops, no Wolverine, no Phoenix, and possibly away from the X-Men in general, to explore who she is without them.