Besides the obvious issue of waiting to see what happens, the problem with long gaps is that readers develop an expectation to how they think the story will go. You’re allowing readers to stew in their own fan theories and when the author does publish the next novel, people become very disappointed because it wasn’t what they initially thought or it fell below the hype.
I am not part of the Game of Thrones fandom but I suspect that’s what’s happening now but the primary offender for this is the Harry Potter series.
Just to clarify before I continue, I love the Harry Potter series. I read Deathly Hallows right before a major exam despite my fear of failure, I loved them that much.
And just like an old person starting off their life lessons to the young, I was with the Harry Potter Fandom when there was that drought between Goblet of Fire and Order of the Phoenix so I know exactly what happens when gaps happen.
People were going off the rails.
All these theories and character attachments. And the pairings, my God the pairings – Harry and Hermione or Ron and Hermione (I’ve always thought Ron and Hermione belonged together, there was no doubt).
And if you guessed enough, something was bound to stick. The R.A.B theory made less of an impact than it should have because fans were collaborating across the globe and reviewing different language editions of novels to check for inconsistencies.
I know authors want to get it right. Writing is an important art form and should be taken seriously. I certainly don’t want some sloppy sequels with plot holes where the writers just pumping them out meaninglessly but I think if the fanbase is too rabid then nothing good can come out of a needlessly long wait.