Updated: Jul 18, 2022
In the early 90s the popularity of this form increased and ultimately reached a peak of sorts. Although around since the late 70s, it's influence as a form subtly crept along behind the scenes, hitting another crescendo in the mid 80s, and then realized a zenith in the 90s with Frank Miller's Batman: The Dark Knight Returns series and other popular titles. I remember The Killing Joke and other cool selections jumping off the page at me while in college.
Such creative revelries put a welcome personal reverie in my life, escape from the classes, presentations, work study jobs, and of course, "parties" (so ubiquitous they were!) and bar hopping during the collegiate years. (Okay, granted some of these forays weren't that bad, perhaps too abundant and readily available in retrospect but...)
I believe the relative popularity of the genre set the stage for the superhero movie craze that began with studios scrambling to capture some of these tales on film, later resulting in the all-encompassing "cinematic universe" model we see for both Marvel and DC in the 2000s.
The form, for me, was a great extension of the dual formats, comics and books. The standard comic books were essentially very short, as we all recall, and the graphic novel made them more enjoyable by increasing the volume of story and the quality of the art. With an increase in quality it made the stories more immersive and "real" for readers I think.